Split namespace, get rid of _real suffix

Split the namespace into UnixOdbcLL (low level) and UnixOdbc (high level). This
way it is possible to use the low level or high level interface, making the high
level interface optional.

Get rid of the _real suffix from all the UnixOdbcLL functions, name conflicts
can be better solved by referencing a function with the namespace prefix
(e. g. "UnixOdbcLL.alloc_handle" instead of "alloc_handle_real")

Add some comments why Handle is translated as long instead of class.