Add SwerveBot example

[megarubber]

Issue #49

Add the SwerveBot example. I added a constants.py file to remove redundant imports, since the original Java example doesn't have a Constants.java.

[auscompgeek]

I added a constants.py file to remove redundant imports

I'm not sure I understand, what would be redundant?

[megarubber]

I added a constants.py file to remove redundant imports

I'm not sure I understand, what would be redundant?

They are mutual top-level imports, because drivetrain.py imports swervemodule.py, and vice versa. I created this file to avoid errors like this:
AttributeError: module 'drivetrain' has no attribute 'kModuleMaxAngularVelocity'

But now, I guess that can be fixed with:
from drivetrain import kModuleMaxAngularVelocity

[auscompgeek]

Oh, you're trying to break an import cycle. Hmm. It seems odd to me that those constants would depend on each other in the example, since that doesn't seem like a physical constraint of real robots.

It looks like in the C++ example they're simply separate constants. Let's do that instead of introducing a constants module.