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/tests/Fixtures/ModuleFixture.cs

@@ -8,7 +8,10 @@ namespace Wasmtime.Tests
     {
         public ModuleFixture()
         {
-            Engine = new Engine();
+            Engine = new EngineBuilder()
+                .WithMultiValue(true)
+                .WithReferenceTypes(true)
+                .Build();
             Store = Engine.CreateStore();
             Module = Store.CreateModule(Path.Combine("Modules", ModuleFileName));
         }