Lower a whole program -- several wap modules -- into one Wax module.
One wasm module comes out, with one flat namespace, because that is what
wasm has. What the module system does is decide the names in it: a
declaration in hashing is emitted as hashing__name, and a reference to
it from elsewhere is written hashing.name.
The modules must arrive in dependency order, which is what
marianoguerra/wap/resolve produces.