Fix help not displaying code correctly

airline_powerline_fonts wasn't wrapped in ><, so it displayed as normal
text and threw off the syntax highlighting.
Fix tagging markup in help

Vim help's help-writing describes how to use '' around options and ||
around help links. Use these where possible to give the correct syntax
highlighting (and help vim-scriptease know the correct type to jump to
for ambiguous symbols).
Merge pull request #250 from pydave/fix-help

Minor improvements to help
fix windows path separator parsing (#251).
refactor helper function to support skinning left and right side (#176).
add tests for theme generate helper functions
add support for showing/hiding tabline based on tab count (#252).
document showing/hiding tabline based on tab count. resolves #252.
for the sourcerers out there... (#254)
tweak default truncation values so 80-width still shows all (#259).
Add option to hide previous/next modes in ctrlp

New option airline#extensions#ctrlp#show_adjacent_modes allows users to
toggle showing the previous and next modes. The default is the same
behavior as before: show the modes.

Add documentation for new option.

These modes are useful if you switch forward and back through ctrlp's
functionality, but they are visual noise if you don't.
Merge pull request #261 from pydave/add-ctrlp-hide-modes

Add option to hide previous/next modes in ctrlp