NameSpace SymbolTable implementation

Implements a data structure to maintain fully qualified symbol name and
name space resolution from partial names.
Merge branch 'StableBranchWithTestcases' of https://github.com/lukechurch/designscript into StableBranchWithTestcases
Merge branch 'StableBranchWithTestcases' of https://github.com/lukechurch/designscript into StableBranchWithTestcases
SymbolTable class update for namespace resolution

- Addressed review comments
- Added few more query methods
Updated some comments
Merge pull request #152 from sharadkjaiswal/StableBranchWithTestcases

NameSpace SymbolTable implementation