Vim: improve JSX filetype detection

Now we detect:

  - Rails assets pipeline files (.js.jsx extension)
  - Any .html or .js file which looks like it contains JSX (we look at
    up to the first 500 lines looking for a hint)

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Vim: add a snippets file for editing HTML

Even though I am using the Emmet plugin for rapid entry of markup, there
are still some constructions that are painful enough to type that it's
worth having a snippet for them. Let's start of with "css", which gives
us a `link` element referencing an external stylesheet.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
tmux: up the history limit by a factor of 8

I just had a spec run that filled up the entire buffer with stack
traces... Checking the memory usage of tmux, I don't see any harm in
letting it retain more lines.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Vim: switch to UltiSnips from snipMate

This includes porting my small collection of personal snippets using the
bundled `convert_snipmate_snippets.py` script, invoked like this:

  bundle/ultisnips/utils/convert_snipmate_snippets.py \
    snippets/spec.snippets > UltiSnips/spec.snippets

(etc...)

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Vim: add supertab

I am not sure I'll keep this; I was playing with UltiSnips and trying to
get an inline-completion menu to appear and wondered if supertab might
help me out, but it doesn't.

Nevertheless, it might be useful, so I'll give it a try.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Vim: conclude supertab experiment

I'm afraid this is too annoying to leave in place. For example, given
code like:

  var foobar = 1,
      baz|

(cursor position indicated with "|"), I'd like to be able to hit tab and
have it move the cursor up to:

  var foobar = 1,
      baz    |

so I can type:

  var foobar = 1,
      baz    = 2;

If there is already a completion for "baz" elsewhere however, it just
sits there.

I'll stick with CTRL-N, which I have pretty well ingrained into the
muscle memory by now.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Vim: consolidate two "script" snippets

The UltiSnips menu is kind of jarring; instead make a single snippet
that enables us to support both expansions (hit delete to remove
optional segment, then <c-j> to move to next tabstop).

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Vim: add 'strict' snippet

Signed-off-by: Wincent Colaiuta <win@wincent.com>