And lots of other miscellaneous changes. Rename InstanceWorld to
InstancePlus and reorganize its contents. This still isn't a great name,
but at least now it has a clear purpose.
This begins reorganizing how translation and compilation occur, and
setting up infrastructure for imports/exports and relocations. It
splits parts out of StandaloneRuntime, forming Module, Compilation,
and Instance structs, which can be used more independently.
It also simplifies the command-line interface, in a step towards
making simple tools that just expose the functionality of the
libraries.
