Thanksgiving 2020 Release

Here's a summary of the commits that went into this release:

• Adds == and != support for joints.
• Removes the following unnecessary and undesirable declarations: JointType alias, UnderlyingType aliases, Voidify class, and the VoidT alias.
• Adds constexpr to more constant declarations and recognizes more non throwing functions with noexcept.
• Improves the underlying dynamic tree code to provide the strong exception guarantee more.
• Improves handling of Joint and Shape construction to provide better compile time messages for any missing required functionality.
• Improves Doxygen documentation to provide better API documentation.
• Adds more unit test coverage.