Move pats options and :LatexTOC out of mappings.vim

Fixes issue #69.

Both the options and the command are now in motion.vim, at hopefully
appropriate places:

- the `g:LatexBox_open_pats` and `g:LatexBox_close_pats` options move into the
  `FindMatchingPairs` function as that is the only place they were used.
- The `:LatexTOC` command is added right at the end, similar to the `:Latexmk*`
  commands in latexmk.vim.