Add new versions of Buffer::get_data().
Fix embarrassing bug in MainLoop::watch_descriptor_readable()/watch_descriptor_writeable().
Fix UdpMulticastSocket::read_noexcept().
Extend UdpMulticastSocket test with some additional checks.
Fix checking value types in Preferences::get() methods.
Add noexcept to callback type definitions in TimerDescriptor, UdpMulticastSocket and Descriptor.