Merge pull request #110 from tuncer/help

Document 'rebar help <CMD1> <CMD2>'
Merge pull request #108 from tuncer/dialyzer

dialyzer_reference plus one minor patch
Always return the errors and warnings from erlydtl

This allows us to use `rebar_base_compiler:ok_tuple/3` and
`rebar_base_compiler:error_tuple/5` when returning from
`rebar_erlydtl_compiler`.