remove usage of fugitive#detect as per request

https://github.com/tpope/vim-fugitive/issues/463
restore original directory change detection. also resolves #474.
Now trailing tabs are also reported, fixed bug when trailings with mixed tabs and spaces were being reported as mixed indents, case when count of spaces at the end of tabbed indentation less then tabstop does not reported as mixed indent anymore.
handle cases where the augroup has not be defined yet. resolves #492
add support for configurable whitespace checking algorithms and default it to the simplest one. resolves #484
provide option to disable runtimepath extension loading. resolves #483
Enable :AirlineToggleWhitespace,

even if g:airline#extensions#whitespace#enabled is disabled
append to the existing value in case the user defined it.
new NrrwRgn integration
doesn't assume user has 'set autochdir' set
fix minor typo in help text
Update README.md vundle installation instructions

[vundle is undergoing interface changes](https://github.com/gmarik/Vundle.vim/blob/master/doc/vundle.txt#L372-L396)
updated nrrwrgn integration
Fix #456

Fix for #456 Status line text color too dim for inactive windows.
add readonly mode so it can be themed independently. resolves #510
static trimming for branch name
#462 -- Support configurable branch name limit.
remove extraneous hash
one logical stmt per line.
Merge remote-tracking branch 'origin/master'