Update solarized colors

Updated to more closely match solarized colors.

Also updated the logic for detecting how many colors a terminal
supports.

The only thing I'm still unsure of is the difference between the 'HEX'
and 'XTERM/HEX' columns on the 'The Values' section of the solarized 
page:
http://ethanschoonover.com/solarized#the-values