Add caching. (#134)

* Allow a module to have a different signature registry than the process-specific

* Add core ability to build compiled code caches

* Remove timing printouts

* Serialize/Deserialize memories to reduce copies

* Work more on api

* Relocate local functions relatively before external functions

* Fix incorrect definition in test

* merge errors caused by merge

* Fix emscripten compile

* Fix review comments

lib/runtime-core/src/structures/map.rs

@@ -8,6 +8,7 @@ use std::{
 };
 
 /// Dense item map
+#[cfg_attr(feature = "cache", derive(Serialize, Deserialize))]
 #[derive(Debug, Clone)]
 pub struct Map<K, V>
 where