add sourcemaps and update to latest module handling

I updated the plugin to use the "macros" option to load in global macros instead of concat'ing a string and added sourcemap support. I also changed it so that it only works with ".sjs" files, and it compiles each file individually to a corresponding ".js" file.

After looking at your repos, you seem to just use a ".js" extension, so I'm open to making this more configurable somehow. I like having ".sjs" which compiles to ".js" and ".js.map" and I get good error handling easily, though I hate that each file is now 3 files.