Adding STMAG and AB mag to flux conversion

[lbardou]

No description provided.

[matthewtownson]

Hi @lbardou,

There is something wrong with our Python 3.5 tests, but there is an error from the Python 2.7 test (see below). Apart from that this looks great!

======================================================================
947ERROR: test_astronomy.test_flux_star_type
948----------------------------------------------------------------------
949Traceback (most recent call last):
950  File "/home/travis/miniconda3/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
951    self.test(*self.arg)
952  File "/home/travis/build/AOtools/aotools/test/test_astronomy.py", line 48, in test_flux_star_type
953    flux = astronomy.flux_star_type(10, 'H', 'A0V', 1.1, 0.2)
954  File "/home/travis/build/AOtools/aotools/aotools/astronomy/_astronomy.py", line 133, in flux_star_type
955    wavelengths = erg_spec[:, 0] * 1e-4
956IndexError: too many indices for array
957-------------------- >> begin captured logging << --------------------
958urllib3.connectionpool: DEBUG: Starting new HTTP connection (1): vizier.u-strasbg.fr:80
959urllib3.connectionpool: DEBUG: http://vizier.u-strasbg.fr:80 "POST /viz-bin/votable HTTP/1.1" 200 3675
960--------------------- >> end captured logging << ---------------------