Add support for dynamic linking to the runtime

[allsey87]

Motivation

In order for WASIX to be an option for software that uses FFI for plugins, some sort of runtime support is needed which enables calls to dlopen, dlsym etc to be handled.

Proposed solution

Similar to Emscripten, I would like to see support in the Wasmer runtime for dynamic linking. I suspect that a similar strategy can be used, however, this will be challenging when it comes to threads etc. (especially when WebWorkers are used to eumulate a pthread-like API).

Alternatives

1. Do not support software that uses FFI for plugins
2. Statically link everything (not really an option for Python without creating very large wasm binaries)