build: add pgmemcache version to Makefile, fixes building without git [#13]

The short version number is now specified in Makefile but the long version
number is still based on git describe output in case we have a proper git
checkout, in the case we don't have a git checkout a `-0-unknown` suffix is
used instead of the git commit information.
doc: update NEWS, README and COPYING

* Minor editing of NEWS entries for versions 2.0 and newer
* Updated README's contact information and credits sections
Merge pull request #14 from saaros/doc

Documentation and build updates