Initial commit

Basic POST and GET callback have been implemented

migrations/2019-02-10-163625_callback/down.sql

@@ -0,0 +1 @@
+DROP TABLE callbacks

migrations/2019-02-10-163625_callback/up.sql

@@ -0,0 +1,5 @@
+CREATE TABLE callbacks (
+  id SERIAL PRIMARY KEY,
+  url VARCHAR NOT NULL,
+  scheduled_date TIMESTAMP WITH TIME ZONE NOT NULL
+)