Improved opening file in existing or new tab.
Used `tab drop` only when gui is available.
Removed `has_gui` variable.
Merge pull request #101 from ricobl/tabnew-drop

Improved opening file in existing or new tab.
Add vimdoc documentation

For now, this is just the README.rst file with appropriate sections. The
content of the file itself is completely unchanged.

Section name suggestions are taken from Steve Losh's Learn Vimscript the
Hard Way [1]. Formatting suggestions are taken from Vim's own
documentation on writing help files (:help help-writing).

The spiffy header was created using the figlet program [2] and the
starwars.flf font found in the figlet fonts database [3].

[1] http://learnvimscriptthehardway.stevelosh.com/chapters/54.html
[2] http://www.figlet.org
[3] http://www.figlet.org/fonts/starwars.flf
Cosmetic and formatting fixes

- Remove images in introduction
- Replace all occurences of VIM with Vim
- Use Vim code blocks
- Surround all keybindings with <>
Document keybindings and options

All keybindings and options have at least a short description added to
them.

With this commit the general structure of a Vim help file is in place.
Add install, intro, and features sections
Add usage section and goto/find_def explanation

The usage section feels sort of superfluous. I don't know. >:(

The distinction between jedi#goto() and jedi#fund_definition() was a bit
unclear, so I expanded it a bit.
Added blurb about configuration in .vimrc

I don't know if this should even be in there because it seems kind of
like a bug.
Merge branch 'vimdoc' of github.com:runiq/jedi-vim into vimdoc