Firebird 3 driver for Python 3 Release 0.8.0

The driver is no longer beta, and is now considered as stable for Firebird 3.0 (support for Firebird 4 is still evolving till final release).

ChangeLog:

Documentation, both in code and separate (especially Usage Guide).

Added support for new FB4 data types in ARRAY fields.

Refactoring in driver hooks.

New Cursor.call_procedure() method.

Refactoring and fixes in Server and its services.