Small spacing fixes like imports in separate lines
for more clarity, and the position of the license.
Cleaned up the class docstring, so it is in only one place
below the class definition. Also small fixes
in the docstrings of the class methods.
The class is now in upper case `Plane` to conform with Python
guidelines. An alias in lowercase `plane` is still provided
for compatibility purposes; this will be deprecated
in the future.
106cd631e0