Markdown indented code blocks (#20473)

* Implement Markdown indented code blocks

Additional indentation of 4 spaces makes a block an "indented code block"
(monospaced text without syntax highlighting).
Also `::` RST syntax for code blocks is disabled.

So instead of
```rst
see::

  Some code
```

the code block should be written as
```markdown
see:

    Some code
```

* Migrate RST literal blocks :: to Markdown's ones

doc/estp.md

@@ -70,138 +70,137 @@ the trace acts like an explanation; in traditional profilers you can only find
 expensive leaf functions easily but the *reason* why they are invoked
 often remains mysterious.
 
-::
-  total executions of each stack trace:
-  Entry: 0/3391 Calls: 84/4160 = 2.0% [sum: 84; 84/4160 = 2.0%]
-    newCrcFromRopeAux
-    crcFromRope
-    writeRopeIfNotEqual
-    shouldRecompile
-    writeModule
-    myClose
-    closePasses
-    processModule
-    CompileModule
-    CompileProject
-    CommandCompileToC
-    MainCommand
-    HandleCmdLine
-    nim
-  Entry: 1/3391 Calls: 46/4160 = 1.1% [sum: 130; 130/4160 = 3.1%]
-    updateCrc32
-    newCrcFromRopeAux
-    crcFromRope
-    writeRopeIfNotEqual
-    shouldRecompile
-    writeModule
-    myClose
-    closePasses
-    processModule
-    CompileModule
-    CompileProject
-    CommandCompileToC
-    MainCommand
-    HandleCmdLine
-    nim
-  Entry: 2/3391 Calls: 41/4160 = 0.99% [sum: 171; 171/4160 = 4.1%]
-    updateCrc32
-    updateCrc32
-    newCrcFromRopeAux
-    crcFromRope
-    writeRopeIfNotEqual
-    shouldRecompile
-    writeModule
-    myClose
-    closePasses
-    processModule
-    CompileModule
-    CompileProject
-    CommandCompileToC
-    MainCommand
-    HandleCmdLine
-    nim
-  Entry: 3/3391 Calls: 41/4160 = 0.99% [sum: 212; 212/4160 = 5.1%]
-    crcFromFile
-    writeRopeIfNotEqual
-    shouldRecompile
-    writeModule
-    myClose
-    closePasses
-    processModule
-    CompileModule
-    CompileProject
-    CommandCompileToC
-    MainCommand
-    HandleCmdLine
-    nim
-  Entry: 4/3391 Calls: 41/4160 = 0.99% [sum: 253; 253/4160 = 6.1%]
-    updateCrc32
-    crcFromFile
-    writeRopeIfNotEqual
-    shouldRecompile
-    writeModule
-    myClose
-    closePasses
-    processModule
-    CompileModule
-    CompileProject
-    CommandCompileToC
-    MainCommand
-    HandleCmdLine
-    nim
-  Entry: 5/3391 Calls: 32/4160 = 0.77% [sum: 285; 285/4160 = 6.9%]
-    pop
-    newCrcFromRopeAux
-    crcFromRope
-    writeRopeIfNotEqual
-    shouldRecompile
-    writeModule
-    myClose
-    closePasses
-    processModule
-    CompileModule
-    CompileProject
-    CommandCompileToC
-    MainCommand
-    HandleCmdLine
-    nim
-  Entry: 6/3391 Calls: 17/4160 = 0.41% [sum: 302; 302/4160 = 7.3%]
-    doOperation
-    forAllChildrenAux
-    pop
-    newCrcFromRopeAux
-    crcFromRope
-    writeRopeIfNotEqual
-    shouldRecompile
-    writeModule
-    myClose
-    closePasses
-    processModule
-    CompileModule
-    CompileProject
-    CommandCompileToC
-    MainCommand
-    HandleCmdLine
-    ...
-    nim
-  Entry: 7/3391 Calls: 14/4160 = 0.34% [sum: 316; 316/4160 = 7.6%]
-    Contains
-    isAccessible
-    interiorAllocatedPtr
-    gcMark
-    markStackAndRegisters
-    collectCTBody
-    collectCT
-    rawNewObj
-    newObj
-    newNode
-    copyTree
-    matchesAux
-    matches
-    resolveOverloads
-    semOverloadedCall
-    semOverloadedCallAnalyseEffects
-    ...
-    CommandCompileToC
-    MainCommand
-    HandleCmdLine
+    total executions of each stack trace:
+    Entry: 0/3391 Calls: 84/4160 = 2.0% [sum: 84; 84/4160 = 2.0%]
+      newCrcFromRopeAux
+      crcFromRope
+      writeRopeIfNotEqual
+      shouldRecompile
+      writeModule
+      myClose
+      closePasses
+      processModule
+      CompileModule
+      CompileProject
+      CommandCompileToC
+      MainCommand
+      HandleCmdLine
+      nim
+    Entry: 1/3391 Calls: 46/4160 = 1.1% [sum: 130; 130/4160 = 3.1%]
+      updateCrc32
+      newCrcFromRopeAux
+      crcFromRope
+      writeRopeIfNotEqual
+      shouldRecompile
+      writeModule
+      myClose
+      closePasses
+      processModule
+      CompileModule
+      CompileProject
+      CommandCompileToC
+      MainCommand
+      HandleCmdLine
+      nim
+    Entry: 2/3391 Calls: 41/4160 = 0.99% [sum: 171; 171/4160 = 4.1%]
+      updateCrc32
+      updateCrc32
+      newCrcFromRopeAux
+      crcFromRope
+      writeRopeIfNotEqual
+      shouldRecompile
+      writeModule
+      myClose
+      closePasses
+      processModule
+      CompileModule
+      CompileProject
+      CommandCompileToC
+      MainCommand
+      HandleCmdLine
+      nim
+    Entry: 3/3391 Calls: 41/4160 = 0.99% [sum: 212; 212/4160 = 5.1%]
+      crcFromFile
+      writeRopeIfNotEqual
+      shouldRecompile
+      writeModule
+      myClose
+      closePasses
+      processModule
+      CompileModule
+      CompileProject
+      CommandCompileToC
+      MainCommand
+      HandleCmdLine
+      nim
+    Entry: 4/3391 Calls: 41/4160 = 0.99% [sum: 253; 253/4160 = 6.1%]
+      updateCrc32
+      crcFromFile
+      writeRopeIfNotEqual
+      shouldRecompile
+      writeModule
+      myClose
+      closePasses
+      processModule
+      CompileModule
+      CompileProject
+      CommandCompileToC
+      MainCommand
+      HandleCmdLine
+      nim
+    Entry: 5/3391 Calls: 32/4160 = 0.77% [sum: 285; 285/4160 = 6.9%]
+      pop
+      newCrcFromRopeAux
+      crcFromRope
+      writeRopeIfNotEqual
+      shouldRecompile
+      writeModule
+      myClose
+      closePasses
+      processModule
+      CompileModule
+      CompileProject
+      CommandCompileToC
+      MainCommand
+      HandleCmdLine
+      nim
+    Entry: 6/3391 Calls: 17/4160 = 0.41% [sum: 302; 302/4160 = 7.3%]
+      doOperation
+      forAllChildrenAux
+      pop
+      newCrcFromRopeAux
+      crcFromRope
+      writeRopeIfNotEqual
+      shouldRecompile
+      writeModule
+      myClose
+      closePasses
+      processModule
+      CompileModule
+      CompileProject
+      CommandCompileToC
+      MainCommand
+      HandleCmdLine
+      ...
+      nim
+    Entry: 7/3391 Calls: 14/4160 = 0.34% [sum: 316; 316/4160 = 7.6%]
+      Contains
+      isAccessible
+      interiorAllocatedPtr
+      gcMark
+      markStackAndRegisters
+      collectCTBody
+      collectCT
+      rawNewObj
+      newObj
+      newNode
+      copyTree
+      matchesAux
+      matches
+      resolveOverloads
+      semOverloadedCall
+      semOverloadedCallAnalyseEffects
+      ...
+      CommandCompileToC
+      MainCommand
+      HandleCmdLine