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/c-api/src/lib.rs

@@ -831,7 +831,7 @@ pub unsafe extern "C" fn wasm_module_new(
 ) -> *mut wasm_module_t {
     let binary = (*binary).as_slice();
     let store = &(*store).store.borrow();
-    let module = match Module::from_binary_unchecked(store, binary) {
+    let module = match Module::from_binary(store, binary) {
         Ok(module) => module,
         Err(_) => return ptr::null_mut(),
     };