Conform to Cargo's conventional file layout

Move `src/*.rs` to `src/bin/*.rs` which are automatically inferred as
binaries and move `src/utils.rs` to `src/lib.rs` which is compiled as a
reusable library for each of the binaries we're building.

src/bin/wast.rs

@@ -0,0 +1,122 @@
+//! CLI tool to run wast tests using the wasmtime libraries.
+
+#![deny(
+    missing_docs,
+    trivial_numeric_casts,
+    unused_extern_crates,
+    unstable_features
+)]
+#![warn(unused_import_braces)]
+#![cfg_attr(feature = "clippy", plugin(clippy(conf_file = "../../clippy.toml")))]
+#![cfg_attr(
+    feature = "cargo-clippy",
+    allow(clippy::new_without_default, clippy::new_without_default_derive)
+)]
+#![cfg_attr(
+    feature = "cargo-clippy",
+    warn(
+        clippy::float_arithmetic,
+        clippy::mut_mut,
+        clippy::nonminimal_bool,
+        clippy::option_map_unwrap_or,
+        clippy::option_map_unwrap_or_else,
+        clippy::unicode_not_nfc,
+        clippy::use_self
+    )
+)]
+
+use cranelift_codegen::settings;
+use cranelift_codegen::settings::Configurable;
+use cranelift_native;
+use docopt::Docopt;
+use pretty_env_logger;
+use serde::Deserialize;
+use std::path::Path;
+use std::process;
+use wasmtime_environ::cache_conf;
+use wasmtime_jit::{Compiler, Features};
+use wasmtime_wast::WastContext;
+
+const USAGE: &str = "
+Wast test runner.
+
+Usage:
+    run_wast [-cdo] [--enable-simd] <file>...
+    run_wast --help | --version
+
+Options:
+    -h, --help          print this help message
+    --version           print the Cranelift version
+    -o, --optimize      runs optimization passes on the translated functions
+    -c, --cache         enable caching system
+    -d, --debug         enable debug output on stderr/stdout
+    --enable-simd       enable proposed SIMD instructions
+";
+
+#[derive(Deserialize, Debug, Clone)]
+struct Args {
+    arg_file: Vec<String>,
+    flag_debug: bool,
+    flag_function: Option<String>,
+    flag_optimize: bool,
+    flag_cache: bool,
+    flag_enable_simd: bool,
+}
+
+fn main() {
+    let version = env!("CARGO_PKG_VERSION");
+    let args: Args = Docopt::new(USAGE)
+        .and_then(|d| {
+            d.help(true)
+                .version(Some(String::from(version)))
+                .deserialize()
+        })
+        .unwrap_or_else(|e| e.exit());
+
+    if args.flag_debug {
+        pretty_env_logger::init();
+    } else {
+        wasmtime::init_file_per_thread_logger("cranelift.dbg.");
+    }
+
+    cache_conf::init(args.flag_cache);
+
+    let isa_builder = cranelift_native::builder().unwrap_or_else(|_| {
+        panic!("host machine is not a supported target");
+    });
+    let mut flag_builder = settings::builder();
+    let mut features: Features = Default::default();
+
+    // Enable verifier passes in debug mode.
+    if cfg!(debug_assertions) {
+        flag_builder.enable("enable_verifier").unwrap();
+    }
+
+    // Enable optimization if requested.
+    if args.flag_optimize {
+        flag_builder.set("opt_level", "best").unwrap();
+    }
+
+    // Enable SIMD if requested
+    if args.flag_enable_simd {
+        flag_builder.enable("enable_simd").unwrap();
+        features.simd = true;
+    }
+
+    let isa = isa_builder.finish(settings::Flags::new(flag_builder));
+    let engine = Compiler::new(isa);
+    let mut wast_context = WastContext::new(Box::new(engine)).with_features(features);
+
+    wast_context
+        .register_spectest()
+        .expect("error instantiating \"spectest\"");
+
+    for filename in &args.arg_file {
+        wast_context
+            .run_file(Path::new(&filename))
+            .unwrap_or_else(|e| {
+                eprintln!("{}", e);
+                process::exit(1)
+            });
+    }
+}