Completed formula parsing and evaluation components. Could do with more testing however.
Documented the parser a bit more.
Added some more documentation. Changed how functions are accessed.
Lexer methods mostly implemented
Moved some things around in the Lexer class, added Lexer unit tests.
Merge branch 'LauraLexer' into jake/GUI
Adds the first version of the GUI, with the ability to save graphs as PNG files. Needs testing on non-Macs.
Fixed the parser up to handle negations properly. Tested charting on Linux.