Updates

[edgararuiz]

• Formalizes 'defaults' functions, and renames them as m_defaults_ to match the pattern of the other internal functions
• Centralizes all calls to the package environment variable that tracks the defaults into the m-defaults.R script
• Re-conceptualizes the tracking object, from a simple way to track the default arguments, but as an overall session variable, which tracks arguments, and also other things such as the cache folder location
• Updates tests and snapshots