chore: move crates into crates/ dir (#1958)

I'd like to tidy up the root a little, and it's nice to have all the
rust crates in one place

crates/atuin-server-postgres/migrations/20220505082442_create-events.sql

@@ -0,0 +1,14 @@
+create type event_type as enum ('create', 'delete');
+ 
+create table events (
+	id bigserial primary key,
+	client_id text not null unique, -- the client-generated ID
+	user_id bigserial not null,     -- allow multiple users
+	hostname text not null,         -- a unique identifier from the client (can be hashed, random, whatever)
+	timestamp timestamp not null,   -- one of the few non-encrypted metadatas
+
+	event_type event_type,
+	data text not null,    -- store the actual history data, encrypted. I don't wanna know!
+
+	created_at timestamp not null default current_timestamp
+);