Generate optimized modules manifest from compiler info

[mstade]

Currently, we look to the file system to find which modules are generated, and thus what to put in optimised-modules.json. However, this should really be information coming from the compiler directly. Indeed, this information may change along the way particularly if a tree shaking linker is used prior to generating the output.

[mstade]

Actually, as it happens, all generated output has to be included in optimised-modules.json, since otherwise we won't get proper module resolution in runtime environments. I'm not sure whether this should just be lib/**/* – it'd certainly be the naive approach, and possibly the right one. Ping @zambezi/ui – thoughts?

[mstade]

This was resolved in #13.