(error during error handling)

also bump version, and add some gettext wraps

and show a somehow helpful error message in this case

fixes whitespace issues, some builtin overrides, and some enormous lines

might make poezio run nanoseconds faster!

(thanks eijebong)

- Load the themes from:
    1 - The sources found in the directory ../data/themes/ (if it
    exists)
    2 - The user-defined dir (or ~/.local/blah)
    3 - The poezio_themes package if found

- Also fix some potential issues with the plugins importer

A command argument can now be completed even if it isn’t the last
one in the input.

- Add a new method Input.new_completion
    Almost like the old auto_completion method, except taht it takes
    another argument: argument_position, which is the argument to be
    completed.
- Methods using the old completion method still work
- All completion methods in poezio now use the new one if necessary
- Further details can be found in the docstring of new_completion

(use new default directory, install the plugins as a separate
python module…)

(also probably fix the I/O operation on closed file issue when using
imp)

- 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