Switch from wabt crate to wast (#434)

* Switch lightbeam from `wabt` to `wast`

Switch from a C++-based `*.wat` parser to a Rust-based parser

* Remove unneeded `wabt` dev-dependency from wasmtime-api

* Rewrite `wasmtime-wast` crate with `wast-parser`

This commit moves the `wasmtime-wast` crate off the `wabt` crate on to
the `wast-parser` crate which is a Rust implementation of a `*.wast` and
`*.wat` parser. The intention here is to continue to reduce the amount
of C++ required to build wasmtime!

* Use new `wat` and `wast` crate names

lightbeam/src/lib.rs

@@ -20,8 +20,6 @@ extern crate lazy_static;
 #[cfg(test)]
 #[macro_use]
 extern crate quickcheck;
-#[cfg(test)]
-extern crate wabt;
 // Just so we can implement `Signature` for `cranelift_codegen::ir::Signature`
 extern crate cranelift_codegen;
 extern crate multi_mut;

lightbeam/src/tests.rs

@@ -1,8 +1,7 @@
 use super::{module::ExecutionError, translate, ExecutableModule};
-use wabt;
 
 fn translate_wat(wat: &str) -> ExecutableModule {
-    let wasm = wabt::wat2wasm(wat).unwrap();
+    let wasm = wat::parse_str(wat).unwrap();
     let compiled = translate(&wasm).unwrap();
     compiled
 }