Add missing files needed for regenerating configure to the distribution;
add MAINTAINERS; improve maintainer-clean to produce a really clean tree.
Signed-off-by: Martin Lucina <mato@kotelna.sk>

* Added a version.sh and relevant changes to configure.in to extract the API
  version from zmq.h at the time autogen.sh is run.
* Moved the version macros to be next to zmq_version in zmq.h and improved
  the comments.
* Modified ZMQ_MAKE_VERSION to use (x) instead of plain x when expanding
  macro parameters.
Signed-off-by: Martin Lucina <mato@kotelna.sk>

Change 'make dist' to generate the Git ChangeLog file, that way it doesn't
have to be manually updated nor kept in Git which causes unnecessary work.

Also change 'make dist' to invoke 'dist-zip' automatically to generate a
ZIP as well as a .tar.gz.

Thanks to http://live.gnome.org/Git/ChangeLog for the inspiration to
automatically generate ChangeLog.

The test suite uses the standard automake support. Tests are always built,
but run only when you do a "make check".