Managed Assets

[sgammon]

It would be really helpful, at the build tool level, and at runtime too, to have a serializable definition for static assets, including their inter-dependencies. This would really help with (1) loading code at runtime (especially via r.js, etc), and (2) saving and restoring build state.

This involves migrating code from earlier versions of Elide, and improving the structure of the asset spec a bit, too.