Improve the atan2 function
Simplified evaluation of atan2
Some more special values of atan2
Remove more argument name confusion
Fix doctests
Improve atan2 special values
Numerically evaluate atan2 for real arguments only
Adapt atan2 tests to refined special values, add test for mpmath evaluation.
Merge pull request #2254 from raoulb/fix_atan2

Fix and extend the atan2 function.