Syntax Check returns a list of tokens now

Changes:
- The enum named syntax_status was moved to a separate header file named
Constants.h
- Evaluator.cpp and Evaluator.h moved to the VS Project directory and
added to the project itself
- Updated the test input with two additional possibilities
- Added a struct called exprToken
- syntax_check() now modifies a passed-by-reference list of exprTokens

None of the new changes are commented yet, but I will do so in a minute
once I can get these to my laptop.