In investigating #799, I also found a related problem with the
pkg-config support.

Macro defines returned by pkg-config were not being handled.  Rather
than proliferating more arguments to the pkg_config function (which
already had too many), I updated it to return a dictionary that's
useful as keyword arguments to `distutils.Extension`.  Since the
values are all lists that will likely need to be "merged" with other
lists, I added a new dict subclass `DistutilsExtensionArgs` that has
default values of `[]`, and has an `update` that knows how to merge in
lists from another dictionary.  This makes the code that uses
`pkg_config()` much more straightforward than it otherwise would be.

Also fixes #799, by properly decoding the output of pkg-config.
Make DistutilsExtensionArgs inherit from collections.defaultdict
Since these files contain non-ascii characters in bytes strings, we should probably have `from __future__ import unicode_literals` at the top.  Also adds a test to detect platforms on which this might fail.
Remove unnecessary 'u' prefix.
Fix #752.  When total == 0, the scale should also be 0, to avoid log(0).
Extract messages from wcslib about rejected (non-standard) keywords and convert them into Python warnings.
Upgrade to wcslib-4.17
Merge pull request #801 from mdboom/setup/pkg-config-bugs

Improve pkg-config support
Merge pull request #817 from mdboom/coordinates/encoding

Coordinates and unicode
Merge pull request #752 from mdboom/utils/progress-bar-exception

ProgressBar(0) raises exception
Fixes #771: Makes the ProgressBar usable as a generator.
Add what's new entry for WCS
Merge pull request #586 from mdboom/wcs/warn_when_relax

Wcs: Warn when encountering non-standard FITS WCS keywords
Merge pull request #771 from mdboom/utils/progress-bar-generator

Make generator version of ProgressBar
implement effhist and helper function
implement tests for effhist
changes in response to comments in PR
changes in response to PR comments
implement wald interval
docstrings; test wald; rename binned_efficiency()