Move TOC syntax highlighting into its own file
Move TOC settings to ftplugin/latextoc.vim

Also add a modeline for code style consistency.
Move TOC keybindings and assorted functions

The functions are moved into the ftplugin/latextoc.vim file because no
other function in the file uses them.
Make all TOC mappings nonrecursive

Just a good thing to do in case the user has some unexpected prior
mappings.
Make ExtractInputs ignore nonexistant .aux files

If an .aux file isn't found by kpsewhich, it is saved as '' in
ExtractInputs()' matches list and subsequently removed with filter().
Fix LatexBox_kpsewhich() behavior

Using :redir results in a number of issues:
- Additional newline(s) in output that have to be stripped out
- Must :redraw! afterwards

Using system() is cleaner. Additionally, the function can be simplified
in the following ways:
- kpsewhich returns either a single filename with a trailing newline, or
  an empty string, so only the last character has to be stripped out if
  a match is found
- LaTeX doesn't handle filenames with newlines (the newlines are
  stripped out), but that's not our problem: we just let Latexmk fail
  accordingly
- kpsewhich doesn't use wildcards, so the glob() call is unnecessary
Move filereadable() check into GetLabelCache()

Now the label completion mechanism completely ignores \@input'ed .aux
files that aren't there.
Fix exploding label cache
Assorted fixes and cleanup

- Remove fnamemodify() call from GetLabelCache(), because it is always
  given an absolute path anyways (either from LatexBox_GetAuxFile() or
  from LatexBox_kpsewhich()).
- Remove unnecessary labels initialization in GetLabelCache().
- Extract labels and inputs in a single buffer
- Remove unused additional argument for CompleteLabels()
Merge pull request #72 from runiq/toc_filetype

Add filetype for TOC
* Moved some TOC-functions to filetype plugin
Added possibility to set aux dir
Merge pull request #74 from runiq/refcomplete_with_include

Fixes label completion with include and inputs.