Improve version numbering management

- allow to define version numbers such as a.b.c(-suffix), where the optional
  suffix parameter may be for instance rc2, beta3 or so...

- deduce the suffix-less release number (a.b.c) since cmake does not support
  release number suffixes...

- improve git-tag matching mechanism. One now searches for the nearest tag that
  matches 'v[0-9]*' and checks if it corresponds to the current release
  number. This allows to define annotate tags that are not related to version
  tags. The only constrain is that such tags must not match 'v[0-9]*'