Make nqp-compiler.js pass a bunch of tests (using a cross compiled setting).

Add NQP::Compiler, HLL::Compiler to nqp-compiler.nqp.
Support negative indexes in array lookup e.g. @foo[-1].
Implement nqp::islt_s.
Implement nqp::radix.
Implement nqp::ctxlexpad.
Implement nqp::ctxouter.
Stub nqp::lexprim.
Implement iterating over contexts.
Set WHO for knowhow STables.
Hashes numify to their number of elements.
Hack to allow numfixing nulls.
Make nqp::unshift work on type objects.
Implement nqp::preinc and nqp::predec.
Disable broken static vars inlining.