Currently it generates a lot of shim functions which delegate to the wasm module
when loaded, but it turns out with `export let` we can just update the bindings!
Instead of exporting a bunch of shims this updates the export functionality to
only update the `export let` directives with the direct values from the wasm
module once the module is done loading.
In addition to being more ergonomic these are much more efficient at reading
large files as they preallocate internally. This provides a nice speed boost
locally, reducing the overhead of `wasm-bindgen-test-runner` from 0.23s to
0.19s, yay!
This commit adds an example of executing the `wasm2asm` tool to generate asm.js
output instead of WebAssembly. This is often useful when supporting older
browsers, such as IE 11, that doesn't have native support for WebAssembly.
Currently errors are reported via Rust panics but there's lots more errors being
added over time so this commit starts the movement towards the `failure` crate
to more idiomatically report errors as well as provide better error messages
over time.
