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
It's useful to make it also return the last term of the sum:
```
tol = 1e-8
for n in ...
    xsum = 0
    for p in ...
        xsum += ...
    if abs(xsum) < 0.1*tol*abs(sum1):
        break
    sum1 += xsum
return sum1, xsum
```