Handle more JS suffixes

[bloodyowl]

At the moment, we can only chose between .js, .bs.js, .mjs and .cjs.

Would it be possible to allow a free definition? For instance I'd like to use .bs.mjs or .res.mjs so that I can ignore them easily in my versioning tool.

[bobzhang]

Note .res.js is a bad idea since it's unclear require ("x.res.") points to x.res.js or x.res.
Would allow .bs.mjs and .bs.cjs fit your use case