doc: correct usage of "inclusive"/"exclusive"

Vim does not consider `t` to be an exclusive motion; we should be
consistent with the Vim documentation.
provide sneak#state() and expose rptreverse. fix #119
fix #121: F/T should be exclusive; also fix {op}vF and {op}vT

Sneak_f and Sneak_t are now fully compliant with Vim's built-in f/t
inclusive/exclusive behavior (see :help inclusive).
Merge remote-tracking branch 'justinmk/master'