makefile: install target, versioning

Set version to 0.1.0 and try to extract an exact version from git tags (none
of which exist at the moment.) The version numbers are going to be used by
upcoming packaging scripts.
packaging: rpm spec file and 'make rpm' target

Allow building RPM packages for recent Fedora, CentOS and Red Hat Enterprise
Linux distributions.  The package spec produces libomcache,
libomcache-devel, python-omcache and python3-omcache packages.