All interface methods implemented, parameters now handled
Switched to using BigInteger where possible to handle exceeding the double limitations.
Switched parser to use Token types rather than Strings.
Merge branches 'LauraLexer' and 'jordan/parser' into LauraLexer

Conflicts:
	MathsThing_GUI/src/uk/ac/uea/mathsthing/Lexer.java
Fixed the parser to allow it to build evaluation trees with functions embedded.
lexer updated to use enums, interface and tests upfated to reflect change
Merge branch 'jordan/parser' into LauraLexer
Fixed the pattern matching being in the wrong order.
fixed lexer regex once more to handle functions properly.
Minor changes to get negation working again.
Now can press "Enter" button on keyboard to draw graph.
Cursor changes to "loading" icon when drawing graph.
Minor bug fixes to parser to account for negative numbers in log and sqrt.
Help HTML page updated with new functions.