add alignTable, parseTableCells to align/format a tab(etc) delimited table (#10182)

* add compiler/unittest_light.nim for easy diffing: assertEquals and mismatch
* fixup
* add alignTable, parseTableCells

tests/compiler/tunittest_light.nim

@@ -0,0 +1,55 @@
+import compiler/unittest_light
+
+proc testAssertEquals() =
+  assertEquals("foo", "foo")
+  doAssertRaises(AssertionError):
+    assertEquals("foo", "foo ")
+
+proc testMismatch() =
+  assertEquals(1+1, 2*1)
+
+  let a = """
+  some test with space at the end of lines    
+
+  can be hard to spot differences when diffing in a terminal   
+  without this helper function
+
+"""
+
+  let b = """
+  some test with space at the end of lines    
+
+  can be hard to spot differences when diffing in a terminal  
+  without this helper function
+
+"""
+
+  doAssert mismatch(a, b) == """
+
+lhs:{
+  some test with space at the end of lines    \n
+\n
+  can be hard to spot differences when diffing in a terminal   \n
+  without this helper function\n
+\n
+}
+rhs:{
+  some test with space at the end of lines    \n
+\n
+  can be hard to spot differences when diffing in a terminal  \n
+  without this helper function\n
+\n
+}
+lhs.len: 144 rhs.len: 143
+first mismatch index: 110
+lhs[i]: {" "} rhs[i]: {"\n"}lhs[0..<i]:{
+  some test with space at the end of lines    \n
+\n
+  can be hard to spot differences when diffing in a terminal  }
+rhs[0..<i]:{
+  some test with space at the end of lines    \n
+\n
+  can be hard to spot differences when diffing in a terminal  }"""
+
+testMismatch()
+testAssertEquals()