Remove parallel testing from Travis, since it is prone to many false positive failures.
Update rotation_matrix to reduce rounding error and correct sign convention on for arbitrary axis
Add explicit rotation_matrix tests
Make angle_axis more consistent and numerically stable (and test)
Add changelog entry
array -> asarray as suggested by @mdboom
Updated tests following @neothemachine's suggestions
Merge pull request #2615 from astrofrog/remove-parallel-travis

Remove parallel testing from Travis
Merge pull request #2619 from eteq/fix-rot-matrix

Fix quirks in rotation_matrix