[Refactoring] Refactoring TextRange to support sub text ranges. Not finished yet!
CodeSharper.Core/Common/ConstraintChecking/Constraints:
  - Fixed some chainability issue
CodeSharper.Core/Texts/TextRange:
  - Moved some methods from TextDocument (e.g.: SubStringOfText, AppendChild etc.)
CodeSharper.Core/Texts/TextRangeHelper:
  - Added a new class for adding new methods to TextRange