* changed parser functionality
* added basic_construct class
* added Node class
* added Symbols and SymbolTable
* added oString which returns string representation of data types
* added FunctionPolicy to abstract sntax tree generation
* modified SymbolTable abstraction
* mem check clean
* added RelationPolicy abstraction
* added ErrorType abstraction to handle error in gdlparser
* added SymbolDecodeStream to smart printing encoded knowledge
* changes to parser file
* added error and warning handling (with printing) in new parser
* added support for clause parsing
* added dependency graph generation
* added bounded variable check to clauses
* added recursive dependency checks
* added definition 15 check
* removed TokenValue
* completed all the required changes in Argument, Fact and Clause
* respective tests are added
* completed tests for KIF
* Added unify module tests
* Shifted core VariableMap to StrVarMap
* shifted DGraph inside namespace core
* shifted ErrorType inside namespace core
* libgdl namespace cleanup
* shifted most of the data types inside core
* added VariableMap to libgdl::core
* completed tests for Unify