Sharing modules between applets

If applets are made of multiple modules with a main module (the one exporting the main function and probably defining the applet properties like its name), then modules may be shared between applets. For example, there could be an `alloc` module that exports its linear memory and an `alloc`, `dealloc`, and `init` functions. All other modules of the applet would import that memory and use those functions.

Open design questions are:
- How is dependency resolution done? Is it described in the applet or modules need to be parsed recursively from the main module?
- How is version management done? If 2 applets depend on different versions of the same module. Should we rely on semantic versioning for modules?
- How is applet management done? Would it become more of a module management with some modules (the main modules) being applets? The CLI should deal with installing/updating/etc modules based on the applet provided on the command line.
- What are the implications of having 2 layers of linking (one linker invocation for each module, then linking those modules in the interpreter)? This may break some assumptions where an applet may look like a binary with a single linking phase.

This may be related to how components work in the component model of WebAssembly, so some answers may be there.