Quote Entities with Double Quotes (#39)

This patch ensures that we actually quote entities (prefix, table name, column name, alias) with double quotes(`"`).
This is important since it allows to use otherwise reserved keywords like `order` to be used.

The tests have been adapted to reflect this change.

Closes #38

Author: Jcambass

lib/ecto/adapters/sqlite3/connection.ex

@@ -1704,7 +1704,7 @@ defmodule Ecto.Adapters.SQLite3.Connection do
     quote_entity(Atom.to_string(val))
   end
 
-  defp quote_entity(val), do: [val]
+  defp quote_entity(val), do: [[?", val, ?"]]
 
   defp intersperse_map(list, separator, mapper, acc \\ [])