This adds version number generation in the build system. Version numbers
follow the format:
<version>-<release>
where release consists of:
<date>-<git-hash>
The version and release numbers are generated by the SCYLLA-VERSION-GEN
script and they are stored in SCYLLA-VERSION-FILE and
SCYLLA-RELEASE-FILE files so that other parts of the build system can
easily pick them up.
For builds that happen from release tarballs, for example,
SCYLLA-VERSION-GEN looks for a "version" file in the tree and just uses
that.
Basically, we're doing pretty much the same as Git is doing in its build
system.
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
