added TruthTableChecker.java class
added tables of correct values conjunction and disjunction
added conditional and biconditional
Merge branch 'master' into TruthTableChecker
Merged from master
Merge branch 'master' into TruthTableChecker
Changed how operator functions work. Wrote formula evaluation for formulas with one operator. Tests included.
Merge branch 'master' into TruthTableChecker
Refactoring. Changed methods for evaluating a formula.
getTopLevelOperators can handle multicharacter operators
Merge branch 'master' into TruthTableChecker
evaluateFormula uses recursion to handle formula with multiple operators
Edited .gitignore and deleted Wff.g4
Merge branch 'master' into TruthTableChecker

Conflicts:
	src/edu/lclark/logic/TruthTableColumn.java
Added negation method to formula evaluation and made a test for it