Added Mechmini 2.0 to Mechmini keyboard folder

Added Mechmini 2.0 to Mechmini keyboard folder

This creates a v1 and v2 subproject.  V1 retains all the same implementations of the bootmapper-ported Mechmnini 1 including #2196.  V2 adds the Mechmini 2.0 kayboard support (I know it took me way to long to get it a pull request in).

All readme's updated to reflect compiling the two seperate keyboards.  Simply either `make mechmini/v1:default` or `make mechmini/v2:defualt`.  Utilizing the rules.mk using `make mechmini:default` will automatically create the Mechmini 2 default keymap as this is the current version and has a much wider user base.