Integrate version numbering into autoconf

configure.in is now the master source for the package version number,
this propagates to src/platform.hpp (for zmq_version) and doc/Makefile.am
(for documentation generation) automagically.

src/config.hpp

@@ -27,11 +27,6 @@ namespace zmq
 
     enum 
     {
-        //  Current version of 0MQ.
-        version_major = 0,
-        version_minor = 0,
-        version_patch = 0,
-
         //  Number of new messages in message pipe needed to trigger new memory
         //  allocation. Setting this parameter to 256 decreases the impact of
         //  memory allocation by approximately 99.6%