Add a chapter about complex numbers
Fix the printing of Re and Im operators

Now they print as the usual Re, Im, in Roman.
Complex: polish few derivations
Fix a bug in atan2(sin x, cos x)
Finish up the derivation of arg(e^z)
Detailed derivation of arg(a*b)
Complex: polish the introduction
Complex: add examples
Remove white space
Fix a bug in example
Add i^i example
Complex: Add Python code for verification
Test complex identities using Python
Merge pull request #27 from certik/complex

Add a chapter about complex numbers