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
This routine could be refactored into two parts:
```
cdef inline double ellip_harmonic_eval(double h2, double k2, int n, int p, double s, double signm, double signn, double *eigv) nogil:
```
and
```
cdef inline double ellip_harmonic(double h2, double k2, int n, int p, double s, double signm, double signn) nogil:
    cdef double *eigv
    cdef double value
    cdef void *bufferp
    eigv = lame_coefficients(h2, k2, n, p, &bufferp)
    if not eigv:
        return nan
    value = ellip_harmonic_eval(h2, k2, n, p, s, signm, signn, eigv)
    free(bufferp)
    return value
```
This then allows moving computation of the coefficients in `_ellip_harm_2.pyx` to be done only once before the integration, which is cheaper.