Nav bug fix

removed a 1px gap between items in nav sub-menu
Added support for md files in watch task

Grunt now watches for markdown changes and re-builds jekyll when it
sees a change. Adding this was pretty self-explanatory.
Design tweaks

Darkened background; removed secondary typefaces; removed accent color
(links now get an underline); slightly narrowed max width
New content added

Split up bio into several separate posts, modified nav to support
sub-menu, added some new images.