Update README.rst changelog.
Remove unnecesary global var.
Simplify settings isolation level to dbspec only.
Add more tests for custom transaction strategies.
Update README.rst changelog with isolation level functions notes.
Remove todo section from README.rst
Update user-guide.rst doc with last isolation-level changes.
Minor code restructuration on main jdbc namespace.
Add transaction management strategy documentation.
Add tests for costom types.
Add user defined types documentation.
Update README.rst