Update mruby
Remove mruby-simple-random, mruby now has a builtin PRNG
Add JSON GEM so we can easier serialise datastructures in the save and load events later.
Add save and load events.

I now simply use the mruby-json gem to serialise the data for
these events, because it eases the process of loading/saving and
allows to support a much wider range of persistable objects.
Note storing integers seems currently buggy, they come back as
floats for some reason.