Implement affine transformations for 2D polygon

[heyvrann]

The following are affine transformations:

1. rotation
2. stretching (we can consider scaling as a special case of stretching)
3. shear
4. translation

This should be a sub-issue of #682.

[yungyuc]

@heyvrann Please make the features available to PointPad and all derived pad classes in C++ and make them available in Python for testing. Each PR uses less than 300-500 lines of code.

When do you plan to have the first PR?

[heyvrann]

@yungyuc Where can I find the PointPad class? I think I need to read that before my implementation. Or should I ask 漢軒 in Discord?

[yungyuc]

See universe/coord.hpp:285 for the class template PointPad. You can find other pad classes (templates) in the same directory.

Just ask anyone in the channel. No need to ask to ask.

[yungyuc]

@heyvrann Please update.