pmt_io: adding string conversion for uniform vectors

Sadly, this needed expansion of unv_template, otherwise I'd have to
hand-write gengen-style code in pmt_io.cc
Initial import of gr-zmqblocks OOT project as-is, prior to rework for in-tree
zeromq: initial surgery to add to master build
zeromq: Initial conversion of include/gnuradio/zeromq files
zeromq: first cut at compiling lib/ directory
zeromq: cleanup and reformatting
zeromq: converted SWIG to in-tree build
zeromq: first try at enabling Python.  Segfaults in SWIG code.
Fix ZeroMQ cmake module.
Fix callback function to work with multiple arguments and return None
in case of error.
zeromq: Fix typo in CMakeLists to link against libzmq
zeromq: Rename "zmqblocks" to zeromq in examples
zeromq: fix import in example
zeromq: renamed sink_pushpull push_sink
zeromq: renamed source_pushpull to pull_source
zeromq: renamed sink_pubsub to pub_sink
zeromq: removed feedback source
wip, renaming and implementing rep_sink
cmake: better setup for finding QWT; otherwise, it can be forced to incorrectly "find" non-existent QWT libs.
filter: updates kernel::fft_filter_xxx documentation to better explain how it works and how to use it in other blocks.

Addresses concern raised in issue #662.