ENH: scipy.special, Implemented Ellipsoidal harmonic function: the first kind, the second kind and normalization constant 

This is an attempt to implement ellipsoidal harmonic functionality. 
The functions implemented are
ellip_harm, ellip_harm_2, ellip_normal
The sources referred to are:
http://www.geology.osu.edu/~jekeli.1/OSUReports/reports/report_499.pdf
http://arxiv.org/abs/1204.0267
And then maybe just make this docstring more extended. The other two docstrings can then have less details (also don't need the same references), and just refer to this one for more details.