Utils: Rename SafeBool to safe_bool (hmm ...)

Fix TAGFILE dependencies
Fix some URL references
PPI: Add additional 'route' documentation
Globally disable SUBGROUPING in Doxygile.global

Provide additional include files for socket protocols
Socket: Change UDP socket handle to bind instead of connect if given an address argument.

Make all include path's relative
Add 'senf/Packets.hh', 'senf/PPI.hh' and 'senf/Socket.hh'

Socket/Protocols/INet: Add INet4Address documentation
Fix some missed INet4Address -> INet4SocketAddress renames
Fixed several std:string arguments to use std::string const &

Socket: Added complete MACAddress class
Packets/DefaultBundle: Make EthernetPacket use the MACAddress class