Restructure project directories (#333)

`/client/web` -> `/frontend`
`/client/cli` -> *delete for now*
`/client/native` -> *delete for now*
`/core/editor` -> `/editor`
`/core/document` -> `/graphene`
`/core/renderer` -> `/charcoal`
`/core/proc-macro` -> `/proc-macros` *(now plural)*

editor/src/communication/mod.rs

@@ -0,0 +1,36 @@
+use std::collections::hash_map::DefaultHasher;
+use std::hash::{Hash, Hasher};
+
+pub mod dispatcher;
+pub mod message;
+use crate::message_prelude::*;
+pub use dispatcher::*;
+
+pub use crate::input::InputPreprocessor;
+use std::collections::VecDeque;
+
+pub type ActionList = Vec<Vec<MessageDiscriminant>>;
+
+// TODO: Add Send + Sync requirement
+// Use something like rw locks for synchronization
+pub trait MessageHandlerData {}
+
+pub trait MessageHandler<A: ToDiscriminant, T>
+where
+	A::Discriminant: AsMessage,
+	<A::Discriminant as TransitiveChild>::TopParent: TransitiveChild<Parent = <A::Discriminant as TransitiveChild>::TopParent, TopParent = <A::Discriminant as TransitiveChild>::TopParent> + AsMessage,
+{
+	/// Return true if the Action is consumed.
+	fn process_action(&mut self, action: A, data: T, responses: &mut VecDeque<Message>);
+	fn actions(&self) -> ActionList;
+}
+
+pub fn generate_hash<'a>(messages: impl IntoIterator<Item = &'a Message>, ipp: &InputPreprocessor, document_hash: u64) -> u64 {
+	let mut s = DefaultHasher::new();
+	document_hash.hash(&mut s);
+	ipp.hash(&mut s);
+	for message in messages {
+		message.pseudo_hash().hash(&mut s);
+	}
+	s.finish()
+}