add an early form of the CompUnitRepo implementation

This is something to play with, and I expect that about
80% of this will land in nom. JVM backend and windows
support deserves more love than it got.
create libraries.cfg if missing
Merge branch 'nom' of github.com:rakudo/rakudo into eleven
build CompUnitRepo on moarv/jvm too
Merge branch 'nom' of github.com:rakudo/rakudo into eleven
fix for flat $/.ast

See https://github.com/moritz/json/commit/601d2a3b13e2f0dbe61a3083b77c69d708c6f133
handle .jar and .moarvm file extensions
add -m wrapper too
consider .jvm/.moarvm candidates besides .pir
choose names that do not hide JSON::Tiny
Merge branch 'nom' of github.com:rakudo/rakudo into eleven
Merge branch 'nom' of github.com:rakudo/rakudo into eleven
Merge branch 'nom' of github.com:rakudo/rakudo into eleven
use nqp::atkey to handle BOOTHash on jvm
Merge branch 'nom' of github.com:rakudo/rakudo into eleven
let CompUnitRepo stringify to absolute path
Merge branch 'nom' of github.com:rakudo/rakudo into eleven
prefere repos with higher priority
replace old dist version when we are reinstalling it
Merge branch 'nom' of github.com:rakudo/rakudo into eleven