NF: added faster implementation of sph_harm in shm.py
TEST: vectorized the for loops
Use scipy sph_harm if scipy version is greater or equal to 0.15.0
Pep 8
BF: python 3 compatibility
Use StrictVersion for checking the version of scipy
Merge pull request #413 from Garyfallidis/faster_sph_harm

Faster spherical harmonics