Added terminus font and urxvt documentation.

How to use terminus and urxvt and still get the powerline glyphs .
Return exception string in place of throwing an exception

Big bunch of `AttributeError`s when renderer failed to be created that renders
vim unusable in case of some of the errors (e.g. invalid configuration) is
annoying.

Conflicts:
	powerline/__init__.py
Use `try/except KeyError` in place of `if in dict/else`
Pop path from self.loaded on exception
Replace self.pl.exception with self.exception

New function is checking for self.pl being set before using logger and also
removes the need of specifying explicit prefix="powerline".

Conflicts:
	powerline/__init__.py
Remove cache before running self.exception, not after
Fix Powerline.exception
Use fallback logger if normal one is not available
detect script directory to make bash and zsh usable without having `powerline` in `$PATH`
Fix git branch name sometimes getting stuck with inotify

If you try to checkout the already current branch in git, git creates
HEAD.lock and renames it to HEAD. This causes the inode of HEAD to
change and so the inotify file watcher stops tracking HEAD.

The fix is to re-create the inotify watch when the file attributes
change. This is a bit of a performance penalty as most of the time the
attribute changes are simple last modified time/size changes, but since
inotify provides no way to know specifically when the inode has changed,
this is the best we can do.
workaround for _powerline_tmux_setenv() issue with bash-4.2.45
Avoid infinite recursion in `POWERLINE_OLD_PROMPT_COMMAND`

Fixes #678
Make clearer the naming conflict in PyPI (closes #681)
Fix weather geoip lookups

- _external_ip() isn't necessary with freegeoip.net as it does this for you when unspecified.
- region_name/country_name make Yahoo's weather API unhappy whereas region_code/country_code work for me (TX/US)
Fix powerline-lint tests

Some notes on the commit:

1. As external_ip and email_imap_alert segments seem to be removed corresponding
   segment_data keys also were removed.
2. Various files that import vim module now have the usual workaround that sets
   vim local to dummy object on error.
3. Syntastic check was failing because it did not specify which highlighting
   groups it uses in documentation. I made it specify them and also moved format
   strings to keywords. Same for some other plugin-local themes.
4. powerline-lint script got --debug argument. Pretty useless currently though:
   it only makes it output traceback for ImportError when failing to import
   module to stderr.
5. Moved themes/vim/plugin/*.json to themes/vim/plugin_*.json.
6. Fixed powerline-lint that ignored problems from values.
Make sure flake8 does not show any errors in powerline/lint/**/*.py files
Set TMUX_PWD_* on startup

Ref #672
Do not mention zpython branch

It is not usable due to some bugs, not maintained and replaced by 
powerline-client
Update dependanceies for Arch packages.
Do not double pl.exception() call, record used pl in variable instead