Merge branch 'release-0.6' into develop
added extra assert to Quaternary1or2._validate_xyz
fixed bug caused by having extraneous commas
added last change to changelog
changed example alloy back to what it was
added several biaxial_strained functions, fixed the example, and wrote some unit tests
Merge branch 'iss39' into develop; closes #39
biaxial_strained functions now take  or
small changes to the strained binaries example, and updated CHANGELOG
added several advanced strained examples; they don't work properly yet, though;
fixed strained alloy mixing, and added another advanced example
small changes to examples
fixed the strain unit tests
fixed build_doc.py, the new examples, and Quaternary1or2._validate_xyz
fixed build_doc to work with new examples
updated CHANGLOG and README
moved hole effective mass calculations to base_material.Base
added previous versions to the CHANGELOG
updated PYPI_DESCRIPTION
bumped version number to 0.7