Packets/MPEGDVBBundle: Use senf::Parse_Variant in SNDUPacket

Packets: Move example policies into .dox files
Packets: Implement variant parser

Utils: Implement ErrnoException

Packets: Add parse helpers for private fields
Packets: Rename all SENF_PARSE_ parse helpers to SENF_PARSER_
Packets/MPEGDVBBundle: Fix parsers to make use of the new parse helper features
Add additional Doxygen predefined macros to correctly parse the packet parse helper macros

Packets: Add parse helper unit-test