Better Wasmtime API for embedder (#287)

* Migrate wasm-rust-api code to wasmtime.

wasmtime-api/Cargo.toml

@@ -0,0 +1,43 @@
+[package]
+name = "wasmtime-api"
+authors = ["The Wasmtime Project Developers"]
+version = "0.1.0"
+description = "High-level API to expose the Wasmtime runtime"
+license = "Apache-2.0 WITH LLVM-exception"
+repository = "https://github.com/CraneStation/wasmtime"
+edition = "2018"
+
+[lib]
+name = "wasmtime_api"
+crate-type = ["lib", "staticlib", "cdylib"]
+
+[dependencies]
+cranelift-codegen = "0.40.0"
+cranelift-native = "0.40.0"
+cranelift-entity = "0.40.0"
+cranelift-wasm = "0.40.0"
+cranelift-frontend = "0.40.0"
+wasmtime-runtime = { path="../wasmtime-runtime" }
+wasmtime-environ = { path="../wasmtime-environ" }
+wasmtime-jit = { path="../wasmtime-jit" }
+wasmparser = "0.36"
+failure = { version = "0.1.3", default-features = false }
+failure_derive = { version = "0.1.3", default-features = false }
+target-lexicon = { version = "0.4.0", default-features = false }
+region = "2.0.0"
+
+[features]
+default = []
+wasm-c-api = []
+
+[dev-dependencies]
+# for wasmtime.rs
+wasi-common = { git = "https://github.com/CraneStation/wasi-common", rev = "8ea7a98"}
+docopt = "1.0.1"
+serde = { "version" = "1.0.94", features = ["derive"] }
+pretty_env_logger = "0.3.0"
+wabt = "0.9.0"
+wasmtime-wast = { path="../wasmtime-wast" }
+wasmtime-wasi = { path="../wasmtime-wasi" }
+rayon = "1.1"
+file-per-thread-logger = "0.1.1"