wishes for mglw.geometry module

[Leterax]

A few wishes I have for the geometry module:

1. quad_2d should probably come with a normal attribute to set the direction of the plane
2. quad_2d has a pos attribute, cube a center attribute. bbox and sphere have neither -> select one consistent name and add it to all objects
3. Rename to either create_xxx or Xxx (create_sphere or Sphere) for a more pythonic interface
4. Rename cube to cuboid/box because it's not a cube
5. cube docs are wrong, they talk about width, height, and depth keywords but that info is in size

Feel free to add other feedback and I will create a PR when I have some free time.

[einarf]

We can't really rename things, but the other suggestions are reasonable. Instead of renaming there can be alias methods, but let's keep that within reason.

[einarf]

Docs are fixed. I'll mark this as "good first issue" indicating that contributions are welcome.