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`
Don't let the vcs detection cross mount point boundaries
Fixes issue 625
Fix UnicodeDecodeError when dir_limit_depth and dir_shorten_len are set
Fix handling of segment include_modes

Segments should only be included if rules for both inclusion and
exclusion are satisfied, satisfying one or the other is not sufficient.

If the include_modes list for a segment is missing or empty consider all
modes to be included so that users do not need to supply an exhaustive
list, since there isn't much point in actually wanting an empty include
list.  Actually check for mode name in the list rather than mistakenly
checking for the segment object.
Handle gitfiles when retrieving branch name

Move code to parse a .git file from the do_status method to a new method
shared with get_branch_name so that branch name can be retreived from
repositories which use a .git file.

Closes #634.
More informative error message. Fixes #638
Make author name ASCII
Merge branch 'fix-setup-unicode-error' into develop
Merge remote-tracking branch 'aschrab/include_modes' into develop
Merge remote-tracking branch 'kovidgoyal/fix-638' into develop
Merge remote-tracking branch 'dbrodie/unicode_path_fix' into develop
Merge remote-tracking branch 'dbrodie/fix_625' into develop