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

tests/instantiate.rs

@@ -5,32 +5,16 @@ use core::cell::RefCell;
 use cranelift_codegen::settings;
 use cranelift_codegen::settings::Configurable;
 use std::collections::HashMap;
-use std::fs::File;
-use std::io;
-use std::io::Read;
 use std::path::PathBuf;
-use wabt;
 use wasmtime_jit::{instantiate, CompilationStrategy, Compiler, NullResolver};
 
-#[cfg(test)]
 const PATH_MODULE_RS2WASM_ADD_FUNC: &str = r"filetests/rs2wasm-add-func.wat";
 
-#[cfg(test)]
-fn read_to_end(path: PathBuf) -> Result<Vec<u8>, io::Error> {
-    let mut buf: Vec<u8> = Vec::new();
-    let mut file = File::open(path)?;
-    file.read_to_end(&mut buf)?;
-    Ok(buf)
-}
-
 /// Simple test reading a wasm-file and translating to binary representation.
 #[test]
 fn test_environ_translate() {
     let path = PathBuf::from(PATH_MODULE_RS2WASM_ADD_FUNC);
-    let wat_data = read_to_end(path).unwrap();
-    assert!(wat_data.len() > 0);
-
-    let data = wabt::wat2wasm(wat_data).expect("expecting valid wat-file");
+    let data = wat::parse_file(path).expect("expecting valid wat-file");
     assert!(data.len() > 0);
 
     let mut flag_builder = settings::builder();