Add ability to format combinator parsers

[tomlanning]

The formatting provided by (Align single-line case statements) is useful, thank-you. It would be nice to have similar formatting for single line combinator parsers (e.g., align the trailing transform definition " ... ^^ { ... }").

For example,

def rule1 = rep(rule2) ^^ { _.mkString }
def rule2 = '0' | '1' | '2' | '3' | '4' ^^ { _.toSomething }

could become,

def rule1 = rep(rule2)                   ^^ { _.mkString }
def rule2 = '0' | '1' | '2' | '3' | '4'  ^^ { _.toSomething }

Might be possible to make this more general and align selected operators in adjacent lines.