Fixes build to report correctly to coveralls.io
Accept multiple - characters before interpolant
Merge pull request #503 from mgreter/feature/coveralls-metrics

Fixes build to report correctly to coveralls.io
Merge pull request #504 from carsonmcdonald/fixfor478

Accept multiple - characters before interpolant
Straightens out some issues introduced with PR#476

The construct in sass_interface.cpp is evil:
source_comments(!c_ctx->options.source_comments)

Fix for omit_source_map_url (never propagated to cpp_ctx)

Removed superfluous source_maps option on struct, generate
source maps when the source_map_file string contains data.