Bump version to 0.3.4

Bump version to 0.3.4

Add add_next_subnet (subnet auto-add)

add_next_subnet tries to add a subnet in a parent subnet,
given the parent subnet and wanted prefixlen.

Signed-off-by: Damien Claisse <[email protected]>

Cleanup and fixes in various areas

- Clean some dead code
- Fix a bug in get_ipnetwork_by_subnet_name that called wrong method inside it
- Remove unnecessary int castings
- Improve coverage to 100%

Initial commit

Signed-off-by: Damien Claisse <[email protected]>