Fixed bug with color256

Previously, the color256 command would make the background color for
affected text black by default. This caused issues when the defined
colors for black and the background differed. It now uses the default
background color.
Added documentation, grep colors, and `om`

om is a function which opens all files which match a grep pattern in
vim, and sets the vim search text to that regular expression.
Made molokai background slightly lighter