Figure out why line numbers aren't reported when there is a parsing error

[avh4]

The code relating to error reporting originally came from elm-compiler, and I haven't looked through most of it yet. Currently if there is a syntax error when parsing, no line numbers are reported. (Also, the filename is not currently reported, but that is a separate issue (see #44).)

Are the positions of parse errors not being recorded by the parser, or are they recorded and not being shown? Does elm-compiler/elm-make even show line numbers for syntax (parse) errors, or only for type errors? What do we need to do to get elm-format to show line numbers when there is a parse error?

[avh4]

Seems to be fixed by #128.