Add additional dependency info
Add Python 3.3 support

Support for unicode literals was reintroduced in Python 3.3 which makes
supporting both Python 2 and Python 3 much easier, so this will be the
minimum supported Python 3 version.

Closes #8.
Remove unneeded extras dependency
Fix various Python 3 related issues

Powerline now detects the Python version and verifies that the user has
Python 3.3 before enabling Python 3 support. To enable Python
3 support, use `python3` to execute source_plugin() in your vimrc
  instead of `python2`.
Add note about Python 3 support in docs
Move string decoding of file name/dir vim segments

Closes #93.
Handle Py2/3 Unicode differences when writing to stdout

Closes #94.
Add side argument in renderer.render() method
Improve side handling in prompt/tmux scripts
Default to no mode in renderer.render() method
Remove unneeded exclusion from MANIFEST.in
Make it possible to return several segment in segment functions

This requires a couple of minor changes to custom segments. The segment
`highlight` key has been renamed to `highlight_group`, and segment
functions must return a list of segments dicts instead of just a dict.

Closes #88.
Add option to set soft divider highlighting group

Closes #89.
Update vim soft divider highlighting
Remove expensive functools.wraps from memoize decorator
Use absolute import in source_plugin.vim

Refs #95.
Return empty string for empty sides
Add exit code/pipe status args in powerline-prompt

Refs #90.
Move branch segment to right side in shell theme
Add zsh prompt script for sourcing in zshrc

This script sets a couple of environment variables in tmux if it's
running, and provides the last exit code and last pipe status to
powerline-prompt. It also traps SIGWINCH and sets the window width as an
env variable in tmux. The default prompt has been split in two and the
git branch is moved to RPS1.

The script must be sourced with an absolute path for now:

    . /path/to/powerline/bindings/zsh/prompt.zsh

Statusline cropping has not been implemented in powerline-tmux yet.

Closes #82.
Closes #83.
Refs #90.