blocks: added gr::blocks::socket_pdu
blocks: added gr::blocks::pdu namespace for PDU functions
blocks: added gr::blocks::pdu_to_tagged_stream
blocks: added gr::blocks::tagged_stream_to_pdu
Merge branch 'master' into next

Conflicts:
	gr-blocks/lib/stream_pdu_base.cc
blocks: added gr::blocks::random_pdu
core: removed PDU related blocks