Injector API restructuring

Injector API:
- Removed socket connection
- Added dynamic API for injections (injection is allowed in all time
after Injector was injected)
- Debugger protocol is extensible now!

Added v8-debug dependence
(Small binary API what allow to extend debugger protocol)
It is not clear to me what is the purpose of the change in the handling of debugger events. There is no unit-tests demonstrating what is the use case where the current implementation does not work. Could you please explain?

It would be best to move this change into a standalone commit (or even a pull request) and include explanation of reasons behind this change in the commit message.

(This comment applies not only to L85, but to all changes made in this file.)