added open_api_page function
Initial version of the astropy.constants docs
Remove tests for futures.
Merge pull request #680 from mdboom/misc/remove_futures_tests

Remove tests for futures
Update CHANGES.rst

Added #666 bug fix.
When passing a value to the env= option of Popen the rest of the environment is not automatically inherited, so we need to make sure to do that.  This could have potentially caused problems on all kinds of systems, but it was especially problematic in Windows where it meant possibly not using the right c runtime dll.
Merge pull request #675 from iguananaut/issue-675

Windows builds failing due to weird crash
Merge pull request #679 from eteq/issue-679

Division of Quantity by a scalar wrong
Merge pull request #556 from adrn/coordinates-ned (with small
modification from eteq/coordinates-ned)
Adds "compose" functionality to units -- it's the converse of
"decompose" and tries to reduce the number of components in a
CompositeUnit.

The Quantity.si and Quantity.cgs methods can then much more easily be
implemented in terms of this functionality.

Also addresses #576 be providing a way for the user to decompose into
a particular system.

Other changes along the way:

  - PEP8-ify quantity.py

  - Privatize the "_simplify" member on units, since it's confusing in
    relation to "compose" and was never meant to be public anyway.
compose no longer requires that it makes progress toward reducing the complexity of the unit as it works.  This allows expressions to me composed into more complex expressions when the set of desired units requires it.  (Point raised by @astrofrog in the PR).  This is a slightly back-to-the-drawing-board approach for compose.
Minor doc fixes
Complete the set of si bases
Allow for factoring by fractional powers.  Also sort results in a way that is most useful (simplest results first).
Rename some documentation files.
Fixups after a rather hairy rebase.
Steradian should not be a unit base.
Fix for Python 2.6 for missing functionality in the fractions stdlib module.
Avoid duplicate results in compose
Fixups after rebase