Separate joint module into separate connections and collision

[bhosale2]

Currently, the implementation for connections and collision lies in joint.py which is a rather non-intuitive name for its contents. A more intuitive name could be connections_and_collision.py? @armantekinalp and @skim0119 suggestions?

[skim0119]

I think collision should be separated. I agree that `connection could be more general name.

[bhosale2]

Ok, then the consensus on this is:

1. Rename joint.py to connections.py
2. Move out collision classes into a separate collision.py

[armantekinalp]

Yes, I think it is a good idea

[Ali-7800]

Merging checklist

• [x] New contact module, Surface base class and tests
• [x] Updated rod-rod, rod-cylinder, self-contact classes, examples, and tests
• [x] Surface subclass: plane, and tests
• [x] Updated rod-plane contact classes (from InteractionPlane and AnistropicFrictionalPlane)
• [x] Updated rod-plane contact classes tests and refactor contact functions in interaction.py and joint.py
• [x] Updated rod-plane contact examples
• [x] Cylinder-plane contact class and tests
• [x] Contact Module Documentation (#331)

[Rahul-JOON]

@Ali-7800 added the New Contact module, surface base class, and tests via #281.

[Ali-7800]

Added Updated rod-rod, rod-cylinder, self-contact classes, examples, and tests via #291

[Ali-7800]

Added the new plane surface subclass.

[Ali-7800]

Added updated rod-plane contact class

[Ali-7800]

Updated rod-plane contact classes tests and refactored contact functions in interaction.py and joint.py

[Ali-7800]

Updated rod-plane contact examples and added continuum snake with lifting wave example

[Ali-7800]

Added cylinder-plane contact class

[Ali-7800]

Updated documentation for contact module, closing now as issue is resolved