Clarify doc for loading custom extensions
minor doc fix: s/various some/various/
improve whitespace detection. resolves #452.
Fix "Cannot use empty key for Dictionary" error

This commit resolves compatibility issue with fugitive plugin. When
using "Gdiff" command on some file, fugitive attempts to open the
current and the index version of the file. For example, if the file is

    /home/taketwo/path/to/the/project/README.md

then fugitive will use the following path to open the index version:

    fugitive:///home/taketwo/path/to/the/project/.git//0/README.md

Opening this file leads to a cascade of errors like this:

    Error detected while processing function
    airline#extensions#tabline#get..<SNR>162_get_buffers..<SNR>162_get_visible_buffers..airline#extensions#tabline#get_buffer_name..airline#extensions#tabline#unique_tail_improved#format:
    line   20:
    E713: Cannot use empty key for Dictionary

The problem is that when a filename like this is being tokenized, there
appear empty "" tokens, and an error occurs when using them as keys in
`path_tokens[token_index]` dictionary. This fix simply skips empty
tokens.
Merge pull request #455 from taketwo/fix-empty-key-error

Fix "Cannot use empty key for Dictionary" error
Customizes tabline appearance: type, close button

This commit adds a couple of new settings so that it's possible to hide
the tab type (all the way to the right) and the symbol which represents
the close button.

The settings and their defaults:

let g:airline#extensions#tabline#show_tab_type = 1
let g:airline#extensions#tabline#close_symbol = 'X'
Improve colour highlights

- Sol: Used a less distracting color to show a modified file/buffer
- Sol: Similar change as above, to tabline as well
- Sol: Warning colour imporved (Previously was some bad shade of magenta)
- Sol: All the Above mentioned changes replicated for CTERM values as well
--------------------------------------------------------------------------
- Luna: `Inactive Modified` colour is improved (Was a shade of red
                                                that was hard to read)
Merge pull request #464 from emilyst/customize-tabline-close-and-type

Customizes tabline appearance: type, close button
Merge pull request #466 from Pychimp/master

Improvements to Sol and Luna themes
Merge pull request #442 from blueyed/doc

Minor doc fixes
filter() result error
My fault, it's a transferred error, add a '\' that' works fine.
Merge pull request #467 from xinleibird/master

filter() result error
Merge remote-tracking branch 'upstream/master'