Use major.minor format in the version string of the sphinx configuration file
Fix print_code_line to respect the UNICODE_OUTPUT configuration variable.
Fixed bug in Model2DKernel
Added type cast to float64 in CustomKernel and adapted peak normalization
Added simple ModelKernel tests
Clarified MexicanHatKernel normalization
Raising exception when normalizing kernels, that sum to zero.
Handle negative luminosity distances in distmod.

* Closes #2008
* Abs lum distances in distmod.
* Add unit test for this behavior.
Update test for non-unicode data
Test code with both unicode_literals and without
First pass at resolving issues when testing with/without unicode_literals
Remove redundant test_*_unicode.py files
Get FITS warning collection working again.
Move to whitelisting
Turn on unicode literal testing in select test files.
Document the TEST_UNICODE_LITERALS tag.
Fix some tests that only fail when running in parallel.
Fix more issues with parallel testing
Document why the test fixtures are defined in conftest.py
line ending/whitespace