Markdown code blocks part 4 (#20189)

No logic was added, just 8 more files have been migrated.

doc/effects.txt

@@ -13,11 +13,12 @@ difficult is the ``newString`` proc: If it is simply wrapped, it
 should not be evaluated at compile time! On other occasions it can
 and should be evaluated:
 
-.. code-block:: nim
+  ```nim
   proc toUpper(s: string): string =
     result = newString(len(s))
     for i in 0..len(s) - 1:
       result[i] = toUpper(s[i])
+  ```
 
 No, it really can always be evaluated. The code generator should transform
 ``s = "\0\0\0..."`` back into ``s = newString(...)``.