Support Unicode "MINUS SIGN" (U2212) in Angle parser.
Output Unicode MINUS SIGN in Unit unicode formatter
For initialisation from list of quantities, default to unit of first
Fix error message to match the truth.
Minor typo fix in documentation; the module is 'angles' not 'angle'.
Slightly alter description of `mag` unit

Previously it was "stellar magnitude", which isn't right because magnitudes are regular used for things that aren't stars.
Added astropy.extern.six to Changes.rst
Fixed imports of pytest
Merge pull request #1470 from mdboom/unit/fix-error-message-about-array-type

Fix error message about acceptable unit scale data types
Merge pull request #1474 from keflavich/patch-2

Added astropy.extern.six to Changes.rst
Merge pull request #1429 from mdboom/misc/unicode-minus

Parsing signs in Angle
Bump our minimum Sphinx version to one that works with current versions of graphniz
Merge pull request #936 from mdboom/docs/minimum-sphinx-version

graphviz syntax error generated by Sphinx 1.2b1
Merge pull request #1475 from astrofrog/fix-pytest-imports-2

Fixed imports of pytest
Merge pull request #1469 from mhvk/quantity-by-list-default-unit

For initialisation from list of quantities, default to unit of first