Change wasm_module_new to use Module::from_binary.

This commit changes the C API function `wasm_module_new` to use the Rust API
`Module::from_binary` which performs verification of the module, as per the C
API spec.

This also introduces a `EngineBuilder` type to the C# API that can be used to
construct an `Engine` with the various Wasmtime configuration options.  This
is required to get the C# tests passing since they use reference types and
multi-value.

Fixes #859.

crates/misc/dotnet/src/WasiBuilder.cs

@@ -5,7 +5,7 @@ using System.Linq;
 namespace Wasmtime
 {
     /// <summary>
-    /// Represents a build of WASI instances.
+    /// Represents a builder of <see cref="Wasi"/> instances.
     /// </summary>
     public class WasiBuilder
     {