Handle the modified filename from parcel

[jeffreypriebe]

Using parcel's output instead of one-off handling ('pug' --> 'html'). I was using other source files (not '.pug') so they came out with their source extension instead of the expected output.

l 93 and removal of special out_flname code.

While here, also output the error message in the emitted error. ll 88 & 115