Reduce timeoutlen to 250

Reduces the timeout to 250 ms in order to mitigate frequent hangs on O line insertion. Has the side effect of punishing slow fingers when running leader commands. Makes VIM feel "snappier" which I suspect is entirely in my head but it does promote hair growth, increased energy, and a pink aura.
http://stackoverflow.com/questions/2158516/vim-delay-before-o-opens-a-new-line