Add a compile command to Wasmtime.

This commit adds a `compile` command to the Wasmtime CLI.

The command can be used to Ahead-Of-Time (AOT) compile WebAssembly modules.

With the `all-arch` feature enabled, AOT compilation can be performed for
non-native architectures (i.e. cross-compilation).

The `Module::compile` method has been added to perform AOT compilation.

A few of the CLI flags relating to "on by default" Wasm features have been
changed to be "--disable-XYZ" flags.

A simple example of using the `wasmtime compile` command:

```text
$ wasmtime compile input.wasm
$ wasmtime input.cwasm
```

src/commands.rs

@@ -1,8 +1,9 @@
 //! The module for the Wasmtime CLI commands.
 
+mod compile;
 mod config;
 mod run;
 mod wasm2obj;
 mod wast;
 
-pub use self::{config::*, run::*, wasm2obj::*, wast::*};
+pub use self::{compile::*, config::*, run::*, wasm2obj::*, wast::*};