Abstract notion of "pre-compiled".

Previously, this has been tied to --target=pir.
Make add_initializations portable to JVM.
Abstract static lexical installation.
First crack at spec'ing REPR compose protocol.
Add compreg and [get|set]_hll_global abstractions.

We're not going to provide full on namespace support in the nqp:: ops.
However, we will provide languages with a global place to stash stuff.
They can hang their idea of namespace off that or any other useful
things (for example, NQP and Rakudo use it to stash their module
loader).
First pass at ModuleLoader portability.

Doesn't do all the things, and some amount of this is going to have
to be VM specific anyway. But this at least starts to clean up some of
what can be stored.
wrote a bit of text about QAST::Want.
allow the use of $(...) in P6Regex
Merge branch 'master' into dyncall-sized-num
Update P6opaque and NQPClassHOW to use new compose protocol.

The old protocol was a list of attribute infos, but the new protocol is a
hash, and that bit of info belongs in the attribute key of that hash, so fix
that.
Bump serialization format version.
First shot at sized int support in P6int.
Update CStruct to new way of doing things.