v0.0.5

Highlights:

• non-allocating momentum_matrix! method
• streamline Mechanism type, including moving body-fixed frame definitions from Mechanism to RigidBody
• add basic documentation using Documenter.jl, including quickstart guide
• add partial support for parallel Mechanisms (kinematic loops)
• add symbolic dynamics example (using SymPy.jl)
• improve @framecheck error message

Fixed issues:

• #110
• #158