Update font patching documentation

Update reference to where fontpatcher.py is located
tmux: Enhance version checking for tmux

tmux configuration has become very fragmented between versions due to a
combination of new features and deprecation of older options. As such,
version checking for tmux became a requirement to allow maximum
functionality along with version-appropriate configuration. However,
wrapping nearly every line with `if-shell` is tedious and becomes
virtually unreadable.

This enhancement to tmux version-checking creates a logical
configuration file structure that reflects the development of tmux. As
additional configurations are added and tmux development continues, this
structure can be leveraged appropriately and extended as needed.

Rather than having multiple `if-shell` checks for the same version, each
version or version group with specific requirements can be checked only
once. This leads to simpler and fewer `if-shell` version checks. It also
reduces the ambiguity introduced by complex `if-shell` commands that
include an 'else' conditional.

A caveat to adding this enhancement is the additional requirement of the
end user to add a tmux variable definition (`POWERLINE_BINDINGS_DIR`) to
his/her `~/.tmux.conf` file. For existing tmux users leveraging
powerline, this may prove to be a slight one-time nuisance immediately
after upgrading. Without this definition, there is no way to determine
the location of the additional tmux powerline config files that have
been added with this enhancement. The docs have also been updated in
this commit to reflect this initial configuration requirement change.
Also added are some additional troubleshooting notes that point to
definition of this variable as a potential issue. Powerline will
continue to work without the definition of `POWERLINE_BINDINGS_DIR`, but
some of the functionality will be reduced and the appearance incomplete
(i.e. colors).

Ultimately, the caveat above is a small price to pay in exchange for a
framework that can be leveraged for proper version-appropriate
configuration of tmux going forward.
Use scripts/powerline-config to source tmux configuration

Ref #872
Use POWERLINE_CONFIG_COMMAND environment variable
Update documentation

Closes #872
Zpython got renamed to libzpython

Not that I wanted this: cmake cannot be told I do not want `lib` prefix. `zsh/` 
prefix in any case should have been removed: zpython is not pretending it is 
a part of zsh now. Keeping old name for those who are still using zpython branch 
(i.e. nearly everybody since zpython got moved less then an hour ago).
Merge branch 'new-zpython-name' into develop
Junk double _POWERLINE_JOBNUM set

_POWERLINE_JOBNUM was already set in precmd, no need to do this again.
Fix pipestatus segment in case of zsh+zpython
Merge pull request #890 from ZyX-I/fix-zpython-bindings

Fix zpython bindings
Add note about lags to troubleshooting-common.rst
Merge branch 'readd-zpython' into develop
Add support for above lines as described in #462

Support is not mirrored in shell bindings yet
Support multiline prompt in bash
Support multiline prompt in zsh

Notes:

- Unlike fish zsh outputs right prompt shifted by one to the left. Which means
  I have to subtract 1 from computed width.
- PS2 and PS3 produce too lengthy prompts when fed with real width. Thus they
  are fed with PS1 prompt width like in ipython (out prompts).
Support multiline prompt in tcsh

Notes:

- I had to launch script twice because tcsh does not actually support multiline
  prompt: it squashes everything into one line.
- Thus I had to add POWERLINE_TCSH_NO_ABOVE_PROMPT: running python twice is not
  nice for performance.
- Due to 1) tcsh shifting rprompt by 1 and 2) tcsh not accepting %{%}-escaped
  color section at the very end of rprompt (actually it is accepting it, just
  makes user input colored as that section) I had to reduce computed width by 2.
- As running powerline command in precmd modifies status code I had to use
  POWERLINE_STATUS variable to save status.
- As tcsh does not accept names that start with underscore non-API powerline
  variables do not start with underscore.
Support multiline prompt in fish

Note: fish does not accept prompt strings that have width identical to the
terminal width: it makes prompt be reduced to just `>`.
Update lint checker
Update documentation
Rename test_configuration to test_provided_config_files