[Rivet] Move bootstrap into main repository for versioning?

[David Grellscheid]

> I have updated GettingStarted now, and at that time found it a bit
> strange to have a 2.0.0/rivet-2-bootstrap script. Should we take this
> opportunity to sort this into
> 
> 2.0.0/rivet-bootstrap
> 2.0.0/rivet-bootstrap-lcg
> 1.9.0/rivet-bootstrap-lcg

OK, I'll do that. Again, please let me know the relevant hex-numbers for
the 1.9.0 option. Should there be a 1.9.0/rivet-bootstrap, too?

  David