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.