This moves from a one-size-fits-all approach for tab expansion to
dictating a default expansion scheme and a per filetype scheme. The
current plugin has custom schemes for Ruby and Makefiles.
Console uses Solarized (Dark) colorscheme, so having a light
background doesn't work well in the console. On the other hand,
the dark background is hard to read in MacVim (for me).
Also delete the forcing of &t_Co to 16 since under tmux, it
automatically detects the 256 colour mode for solarized and is therefore
no longer necessary.