Add ExpressionBuilder to phase field module (#3927)
Document ExpressionBuilder (#3927)
Rework substitution to make it not stupid (#3927)
Work around shoddy compiler error analysis (#3927)
Pass by reference, add single bracket convenience functions (#3927)
Implement binary operators on functions (#3927)
Overloading operators up the wazoo! (#3927)
Fix associativity at equal precedence (#3927)
Merge pull request #3930 from dschwen/expbuilder_3927

Add ExpressionBuilder to phase field module