Merge pull request #21 from MathMagique/master

Made const placement consistent (const placed after type it refers to). ...
Added include to fix compilation errors on OSX
Unified the execute_python_code_* functions in the test suite.
Using the new execute_python_code_* functions.
Fixed indentation.
Added some documentation.
Added Python include to avoid compiler problems on OSX.
Using "not" in place of "!"
Merge pull request #22 from abingham/unify_exec_python

Unify exec python