Add foreign local themes support

Refs #3.
Update README
Install tmux/prompt files as scripts
Update terminal rendering for bash
Add usage instructions for terminal/tmux
Fix font patching instructions for OS X

Closes #46.
Add troubleshooting info for iTerm2 question mark issue

Closes #27.
Refs #48.
Add troubleshooting info about NameError in MacVim

Refs #48.
Add troubleshooting info about OSX ImportError

Closes #39.
Escape command in prompt usage instructions
Update terminal prompt usage instructions

Closes #56.
Reset highlighting at end of rendered result

Closes #57.
Rename weather segment
Add humanize_bytes function to library
Add imports to lib init file
Add network load tmux segment
Don't explicitly reset tmux attributes
Remove example tmux.conf
Add PowerlineSymbols font file

On Linux it appears to work perfectly to just have this font file
present on the system as it automatically chooses fallback fonts if
a glyph isn't present in the current font.
Update font installation instructions

Refs #60.