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
Do not double pl.exception() call, record used pl in variable instead
Don't show '//' when using path separator

Currently, the cwd segment is showing //etc when we are in /etc and / when we are in the root file.
This small patch fix this
Fix display for home directory
Add Meslo fonts to the fontconfig file
New fixed segment showing position of current view

Solves #539
Fixed version of #540 and #579
Works now for split windows and wrapped lines.
Replace POWERLINE_OLD_PROMPT_COMMAND with the code used by [z][1]

Does not fix anything, but is three lines less and is probably the way other 
tools expect us to do.

[1]: https://github.com/rupa/z
Replace `jobs` with `jobs -p`


If some long shell code is run in the background it may be shown as more then 
one job:

    bash-4.2$ {
    > echo abc | while read line ; do
    > sleep 1s
    > sleep 1s
    > done
    > } &
    [1] 9401
    bash-4.2$ jobs
    [1]+  Running                 { echo abc | while read line; do
        sleep 1s; sleep 1s;
    done; } &

`jobs -p` print exactly one job in this case.
Document problem found when exploring #749
Fix functional shell tests in travis

Hostname in travis contains random numbers meaning that it occasionally may 
contain a PID as well. Thus it must be replaced first.
Merge pull request #754 from ZyX-I/improve-bash-bindings

Improve bash bindings
Add powerline/bindings/fish/powerline.fish
Make fish bindings feature complete, add documentation

Added features:
- Updating TMUX_PWD_* when PWD variable changes
- Updating TMUX_COLUMNS_* when WINCH signal is received