Option to return full source map object instead of toJSON() version about css

[conradz]

What use would you have for the SourceMapGenerator object that is used by the compiler? To create a SourceMapConsumer object you need the serialized object (like what is produced with toJSON) anyway, so I'm not sure what use the SourceMapGenerator object is. (I could be missing something though.)

[harthur]

You can create a consumer from a generator with var consumer = SourceMapConsumer.fromSourceMap(generator) and it won't serialize the mappings.

[lydell]

Postcss used to behave exactly like this module, but changed to work like @harthur suggests in version 1.0. See postcss/postcss#49 (comment) for a bit of discussion on it. Perhaps this is something we should consider for 3.0?

[conradz]

I think it is something that won't be widely used, and I would encourage people to use the JSON object representation, since that is more stable than the SourceMapGenerator API.

Maybe we could return the source map generator if sourcemap: 'generator' is specified? This would be backwards compatible since when sourcemap: true is specified we would still return the object representation.