Configure the namespace of the imports functions

[YaronWittenstein]

Currently, the NewImports() hard-codes the import namespace as env.

If we compile a Rust program to WASM file, then the Rust compiler also hardcodes the
import namespace as env too (so the current wasmer go binding the Rust wasm output files play well together)

However, if we patch a wasm file import namespace to something else (different than env), then we won't be able to use it via the golang wasmer binding

Proposed solution

Instead of

imports, _ := wasm.NewImports().Append("sum", sum, C.sum)

Have this API:

imports, _ := wasm.NewImports().Append("my_namespace",  "sum", sum, C.sum)

Thank you! @Hywan :)

[Hywan]

Thanks for the proposal!

What do you think about this API:

wasm.NewImports().
    Namespace("env").
        Append("sum", sum, C.sum).
        Append("f", f, C.f).
    Namespace("wasi").
        Append("log", log, C.log)

Would you like it? It's more like a tree. Append uses the last defined Namespace.

[YaronWittenstein]

@Hywan that's even better!
It makes more sense since usually, all the imports will be for 1-2 namespaces while the number of functions will be much bigger)

I guess the default namespace will be env

[Hywan]

Correct, env will be the default namespace.