[WIP] Big Restructuring: Embedded AST

Now espower embeds target AST substree and tokens into output, and using subpath notation to point them.

* [x] Re-Design
* [x] Spike
* [x] Update espower to 0.6.0
* [x] Update dependencies
* [x] Rough implementation
* [x] Maint tests
* [ ] Prepare for next minor release