Refactor build system to remove sub-library dependencies

senfscons: Speed up non-documentation builds (doesn't help much)
Socket/Protocols: Add documentation for sockaddr_cast

Packets: Implement 'ids()' option for SENF_PARSER_VARIANT
Packets: Update DTCPPacket to use the new SENF_PARSER_VARIANT features
HowTows/NewPacket: Adjust for new SENF_PARSER_VARIANT

Console: Documentation

Console: Implement OverloadableCommandNode
Console: Make all virtual functions private
Console: Rename ObjectDirectory to ScopedDirectory
Console: Move non-template dependent ScopedDirectory members to ScopedDirectoryBase
Console: Provide owner-less void specialization of ScopedDirectory

Packets: change *_RO field helper macros to add a private r/w accessor
senfscons: Introduce TEST_EXTRA_LIBS variable and move BOOSTFSLIB there
Socket/Protocols/INet: Make INet[46]MulticastSocketProtocol inherit MulticastSocketprotocol
Change SENF_NO_DEBUG to SENF_DEBUG

doclib: Introduce an intermediate doxygen-compatible image map format
Update all image maps to the new format

PPI: Add missing unit-test for typed connectors and fix typed connectors implementation
Socket: Remove left-over log message

debian: Add missing call to build arch packages
debian: Exclude '_template' dir from the source package
doclib: Fix 'dot' script to work with more doxygen versions

debian: Optimize build process (compile in build stage not in binary stage)

doclib: Fix some senf.css / doxygen.css interactions
Packets: Implement ConcreatePacket::parser
Packets: Make the PacketTypeMixin work with (simple) dynamically sized parsers

Packets: Renamed PacketParserMixin::registry_key_t to key_t
Packets: Add PacketParserMixin::lookup helper

admin: Make build.sh do a parallel build and use 'nice'
admin: Make build.sh import an optional DOXYGEN envvar
senfscons: Allow setting arbitrary simple build environment variables from the command line

HowTos/NewPacket: Started the packet type section
doclib: Implemented the '\autotoc' command
Packets: Add SENF_PACKET_REGISTRY_REGISTER macro

doclib: Find optimal graph rotation for large dot graphs
doclib: Break long pathnames in dot graphs
doclib: Use new DOT_GRAPH_MAX_NODES parameter in Doxyfile.global
doclib: Break lines in (textual) class inheritance lists

Examples: Autogenerate Mainpage.dox
HowTos/NewPacket: Start new howto