parsing now works almost perfectly
Merge branch 'Yoav_working_parser' into merge_yoav

Conflicts:
	src/webwork/expr_parser/.ipynb_checkpoints/Study Parsing And Edit Distance-checkpoint.ipynb
	src/webwork/expr_parser/Eval_parsed.py
	src/webwork/expr_parser/Study Parsing And Edit Distance.ipynb
	src/webwork/expr_parser/parsetab.py
	src/webwork/expr_parser/webwork_parser.py
Incorporate Yoav's fixes into webwork_lexer.py
Committing ply output stuff