Updated documentation, comment about synctex

Added a short note about setting synctex option through
g:LatexBox_latexmk_options, as suggested in #95.
Added some refs to docs for #95
Add option to make the quickfix window not active

One can do
`let g:LatexBox_quickfix=2` to make the quickfix window not
active when shown: the cursor then stays in the current window.

Also correct a typo in the doc.
Some clean-up of doc file

Fixed some typos, made tags correctly right-aligned, and made setting entries
more consistent.
Some minor updates