Set encoding to UTF-8
Add FITSImage.ra()
Add unit test for FITSImage.ra()
Add FITSImage.dec()
Add unit test for FITSImage.dec()
Read right ascension with FITSImage.ra()
Read declination with FITSImage.dec()
Update description of --rak
Update description of --deck
Add support for sexagesimal coordinates

The --rak and --deck options have so far expected the coordinates to
be in decimal degrees — the most common (and arguably also optimal)
format in which to store celestial coordinates. However, as seen in
#36, some FITS images use a sexagesimal representation. In fact, the
Dictionary of Commonly Used FITS Keywords [1] mentions hh:mm:ss[.sss]
and dd:mm:ss[.sss] as another format in which the right ascension and
declination, respectively, may be expressed.

[1] http://heasarc.gsfc.nasa.gov/docs/fcg/common_dict.html

This merges branch 'sexagesimal-coordinates'