Implementation of map2alm_spin
Implementation of alm2map_spin
Import alm2map_spin,map2alm_spin in base namespace
Order of the arguments was wrong
map2alm_spin and alm2map_spin unit tests

Implemented by Duncan Hanson
* Compare spin-1 alm2map transform to alm2map_der1
* Compare spin-1,2,3 alm2map and map2alm transforms to precomputed
  values for small lmax,nside and spins=1,2,3.
* Compare forward and backward transforms (not very stringent,
  they only agree to ~1.e-2, because healpix is not complete basis).
Restored spin0 test
Fix for spin0

The C++ code assumes arrays are initialized to zero.
Merge pull request #76 from zonca/alm2map_spin

implement alm2map_spin and map2alm_spin