Add a model for posts

migrations/2018-04-23-132822_create_posts/down.sql

@@ -0,0 +1,2 @@
+-- This file should undo anything in `up.sql`
+DROP TABLE posts;

migrations/2018-04-23-132822_create_posts/up.sql

@@ -0,0 +1,10 @@
+-- Your SQL goes here
+CREATE TABLE posts (
+    id SERIAL PRIMARY KEY,
+    blog_id INTEGER REFERENCES blogs(id) ON DELETE CASCADE NOT NULL,
+    slug VARCHAR NOT NULL,
+    title VARCHAR NOT NULL,
+    content TEXT NOT NULL DEFAULT '',
+    published BOOLEAN NOT NULL DEFAULT 'f',
+    license VARCHAR NOT NULL DEFAULT 'CC-0'
+)