Include the quickfix title in the statusline

The quickfix title often has useful information about how it was
invoked. Include it in the statusline.
Merge branch 'fix-quickfix-title' of https://github.com/pydave/vim-airline into pydave-fix-quickfix-title
account for possible undefined variable.
use the same fugitive check as the extension.
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).