Switch DB from sqlite to Postgres

-Postgres for production
-Migrations don't translate well between sqlite and postgres, better to just develop using the same database as production.
-Fixed migrations to work with Postgres
-Updated Readme for PG install instructions
-database config moved to .example

config/database.yml.example

@@ -0,0 +1,23 @@
+development:
+  adapter: postgresql
+  database: velocipede
+  username: velocipede
+  password:
+  host: 127.0.0.1
+
+# Warning: The database defined as "test" will be erased and
+# re-generated from your development database when you run "rake".
+# Do not set this db to the same as development or production.
+test:
+  adapter: postgresql
+  database: velocipede
+  username: velocipede
+  password:
+  host: 127.0.0.1
+
+production:
+  adapter: postgresql
+  database: velocipede
+  username: velocipede
+  password:
+  host: 127.0.0.1