WIP:  Documentation Improvements

Preview:
http://www.stsci.edu/~lbradley/photutils/
Lines 2-7 (including the style) are used to hide the <h1> header in lines 9-11.  Lines 1-11 are basically a trick that allows all of the following section headers (now <h2> because of the present, but "hidden" <h1>) to be underlined.  But I could probably do the same thing by adding the underline style to <h1> and reducing the font size.....that's probably more clear of the intent.