Add current snapshot1 WASI spec as test + fixes (#31)

* Add WASI spec (minus unions)

* Fill in all WASI shims

* Clean up derives and fix noncopy struct write method

This commit does three things:
* it uses the full, current snapshot1 WASI spec as a compilation test
* it fixes noncopy struct write method (which was incorrectly resolved
  in certain cases to the inherent method of the `GuestPtrMut` rather
  than the interface method `GuestType::write`
* it cleans up derives for structs and unions which should not auto-derive
  `PartialEq`, `Eq`, or `Hash` since their members are not guaranteed to
  be compatible

crates/generate/src/types/struct.rs

@@ -50,7 +50,7 @@ fn define_copy_struct(names: &Names, name: &witx::Id, s: &witx::StructDatatype)
 
     quote! {
         #[repr(C)]
-        #[derive(Copy, Clone, Debug, ::std::hash::Hash, Eq, PartialEq)]
+        #[derive(Copy, Clone, Debug, PartialEq)]
         pub struct #ident {
             #(#member_decls),*
         }
@@ -185,12 +185,12 @@ fn define_ptr_struct(names: &Names, name: &witx::Id, s: &witx::StructDatatype) -
         let name = names.struct_member(&ml.member.name);
         let offset = ml.offset as u32;
         quote! {
-            self.#name.write(&location.cast(#offset).expect("cast to inner member"));
+            wiggle_runtime::GuestType::write(&self.#name, &location.cast(#offset).expect("cast to inner member"));
         }
     });
 
     quote! {
-        #[derive(Clone)]
+        #[derive(Clone, Debug)]
         pub struct #ident<'a> {
             #(#member_decls),*
         }

crates/generate/src/types/union.rs

@@ -71,7 +71,7 @@ pub(super) fn define_union(names: &Names, name: &witx::Id, u: &witx::UnionDataty
     if !u.needs_lifetime() {
         // Type does not have a lifetime parameter:
         quote! {
-            #[derive(Clone, Debug, PartialEq)]
+            #[derive(Copy, Clone, Debug, PartialEq)]
             pub enum #ident {
                 #(#variants),*
             }
@@ -112,7 +112,7 @@ pub(super) fn define_union(names: &Names, name: &witx::Id, u: &witx::UnionDataty
         }
     } else {
         quote! {
-            #[derive(Clone)]
+            #[derive(Clone, Debug)]
             pub enum #ident<#lifetime> {
                 #(#variants),*
             }