Write documentation

[bendem]

• Javadoc all the things
• Getting started
• Explain how mapping works
• Explain how datasources work (setup)
• Explain how AutoCloseable is used
• Explain how Transaction works
• Mention where jdbc primitives are closed
• Mention goals of the lib (you write the sql, I handle jdbc)

[bendem]

Probably also needs a "getting started with " section. Like an example on how to make it work with spring @Transactional for example.