Source map support

[BasixKOR]

It seems like this plugin has no support for sourceMap option (yet), so I thought it would be nice to have a issue tracking it.

[slig]

Hi,

I'm not using this plugin anymore, so if you or someone else would like to work on this issue, it'd be appreciated.

[BasixKOR]

I'm working on this issue, Please review my PR after I submit it if you have time!