chore(espower-coffee): add convert-source-map and update espower-source to support sourcemaps
feat(espower-coffee): interact with coffeescript compiler to adjust line number in power-assert output
refactor(espower-coffee): avoid generating unnecessary sourcemaps if path does not match
docs(README): update README (see the line number in output is correct)
Merge pull request #1 from twada/sourcemaps

support sourcemaps