- Try to reduce the use of the “core” object in the plugins
- New “api” member for each BasePlugin which is a wrapper around
    the unique PluginAPI object. (instead of having the methods
    directly in BasePlugin and then calling the PluginManager)
- Documented methods with rst (for sphinx)

(while staying backwards-compatible)

Importlib is utterly broken in python < 3.3, So revert for now

This reverts commit a1c3d0dc.

Conflicts:
	src/plugin_manager.py

We were using the deprecated imp methods, now we use importlib

Also add a simple translator module