Initial release of redshifts

The first release of the redshifts package. Main features include:

• Flexible search within a radius of a given set of (RA, DEC) coordinates
• Uses column names and descriptions (including UCD keywords) to identify columns containing spectroscopic redshifts or velocities
• Weeds out photometric redshifts and duplicates and returns a unique list of "best" spectroscopic redshift measurements.