Accidentally left removed #434 when I meant to add it back in! Updates
the `wast` crate dependency and adds support for translating
`v128.const` instructions to a `RuntimeValue`
Closes#441
* 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
This change adds an `--enable-simd` flag to the binaries in this project. This allows the ISA `enable_simd` flag to be set and to configure the validation configuration used by wasmparser to allow SIMD instructions.
