Do not override Powerline.setup(), use .do_setup() for this

Same reason as for `.__init__()` which was replaced by `.init()`
Import sys in reload() function

It may be None sometimes
Implement powerline reloading in libzpython bindings
Add powerline-reload function for libzpython bindings
Rename Ipython to IPython (two capital letters in place of one)
Refactor IPython bindings

- Replaced two powerline objects with one powerline object utilizing
  RendererProxy proxy class that holds two Renderer instances.
- Made .setup() functions do something more meaningful.
Add `%powerline reload` IPython magic function
Update documentation
Merge pull request #1000 from ZyX-I/non-vim-reload

Add powerline reloading support to IPython and zsh with libzpython