PostgreSQL support. Configure options array. Issue #10 resurrected: custom jobs table name.

Decided to implement couple of stuff, here's a breakdown:
* **PostgreSQL support**: Generalize some MySQL specific code to work on both engines. Created a new .sql file for PostgreSQL jobs table creation, and also a specific test file.
* **Implemented _configure_ to take options array**: Was on the todo list of the repository. At the same time, revamped the connection parameters to be more generic (no need for specific MySQL type of connection parameters anymore).
* **Resurrected issue #10**: Since I was at it in doing a couple of changes, thought this one was worth the effort ;)

SQLite support is something that I thing it could be useful, but early investigations lead me to delay it, due to heavy changes in SQL code (bulk enqueues mainly).