Update memoize class and add support for persistent cache
Create tmux segments

Refs #44.
Cleanup Python files to comply better with PEP 8

Removed excessive newlines and comments, and fixed whitespace issues.
Merge branch 'develop' into feature/tmux

Conflicts:
	powerline/ext/tmux/segments.py
Rename default colorscheme
Add right/left options to tmux script
Create neutral tmux colorscheme
Enable tmux segments
Merge branch 'feature/tmux' into develop

Closes #41.
Closes #43.
Closes #44.
Add Liam Curry to contributors list

Refs #44.
Separate colorschemes by extension

Refs #45.
Make mode_translations optional in colorschemes
Move tmux example into extension directory
Use midline ellipsis for dir shortening
Update terminal renderer output depending on shell

Bash and zsh have different ways of escaping colors in the prompt, this
update checks the $SHELL environment variable and uses the correct
escape sequence for the current shell.

A known issue with this method is that $SHELL doesn't get updated when
switching shells (i.e. if you're running /bin/bash when you're in a zsh
shell) so in rare cases rendering errors may occur. A workaround which
is much slower is to parse the output of `ps -p $$` which always returns
the current shell.
Add foreign local themes support

Refs #3.
merging with original