Big Restructuring: Canonical Assertion

Now espower generates canonical assertion expression from AST instead of searching/splitting JavaScript source code.

This feature enables us to instrument power-assert feature on multiline assertion expression.
And, Embedded AST is not required any more.

TODO
----------
- [x] Spike
- [x] Update espower to 0.7.0
- [x] Update other dependencies
- [x] Remove Embedded AST feature
- [x] Maint tests
- [x] Prepare for next minor release