Fix tiny typo in docs

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Switch selection highlight color for better readability

As suggested by André Arko here:

  https://wincent.com/issues/2055

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Make selection highlight color configurable

A few comments on this commit:

  https://github.com/wincent/Command-T/commit/d30099cac79dfdbc4a16d

suggest that there is no "one size fits all" selection highlight color
that's going to work for everybody.

Make it configurable.

Signed-off-by: Wincent Colaiuta <win@wincent.com>