Big repository reorganization

The code is divided in three crates:
- plume-common, for the ActivityPub module, and some common utils
- plume-models, for the models and database-related code
- plume, the app itself

This new organization will allow to test it more easily, but also to create other tools that only reuse a little part of
the code (for instance a Wordpress import tool, that would just use the plume-models crate)

plume-models/src/post_authors.rs

@@ -0,0 +1,26 @@
+use diesel::{self, PgConnection, QueryDsl, RunQueryDsl, ExpressionMethods};
+
+use posts::Post;
+use users::User;
+use schema::post_authors;
+
+#[derive(Queryable, Identifiable, Associations)]
+#[belongs_to(Post)]
+#[belongs_to(User, foreign_key = "author_id")]
+pub struct PostAuthor {
+    pub id: i32,
+    pub post_id: i32,
+    pub author_id: i32
+}
+
+#[derive(Insertable)]
+#[table_name = "post_authors"]
+pub struct NewPostAuthor {
+    pub post_id: i32,
+    pub author_id: i32
+}
+
+impl PostAuthor {
+    insert!(post_authors, NewPostAuthor);
+    get!(post_authors);
+}