Move compiler checks and passes out of |PEG.Compiler| definition
Move compiler checks and passes out of |PEG.Compiler| definition

This allows splitting them into separate files in the future. It also
decreases indentation level in the code.

GerHobbelt/pegjs,wwall/pegjs-fn,wwall/pegjs-fn,Mingun/pegjs,mcanthony/pegjs,mcanthony/pegjs,pegjs/pegjs,crguezl/pegjs,luisvt/pegjs,GerHobbelt/pegjs,Sciumo/pegjs,luisvt/pegjs,crguezl/pegjs,Mingun/pegjs,jlturner/pegjs,Sciumo/pegjs,jlturner/pegjs,pegjs/pegjs