Serialize and deserialize compilation artifacts.

[yurydelendik]

Fixes #1779

This is final patch in series to allow direct access to the compiled code.

• Added compile_and_serialize API function that allows to save CompilationArtifacts object in binary format (+target/config fingerprint)
• Added unsafe Module::deserialize API function that allows to read the above data and create Module object. Marked unsafe since it does not provide any guarantees for safety of the ingested code.
• Portability limitation is that producer and consumer'sConfigs must have the same host triple, codegen flags, and Tunables. (Can we ignore CompilerStrategy?)

PR opened for feedback.

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[alexcrichton]

Nice!

I think that we'll want to expand the documentation on these functions as well. I'd probably pick one of serialize/deserialize and add a bunch of docs there, referencing these docs from the other function instead of duplication as well.

In terms of documentation contents I think we'll want to document how the bytes are intended to be used, for example they're only usable by one version of the wasmtime crate, they're not intended to be long-lived artifacts. Also we'll probably want a small example in the documentation of serializing/deserializing.

Can you be sure to add some Rust tests as well?

[alexcrichton]

Sorry missed the updates here but this all looks good to me now!