* gemspec adjusted to install only libraries related to a version (v4 or v5)
* select sisu version to create, build & install

* rake gemcbi #(create build install sisu gem)
* rake gemspecscreate && \
  rake gembuild && \
  sudo rake geminstall
* rake gemspecscreate && \
  gem build sisu5.gemspec && \
  sudo gem install --no-rdoc --no-ri \
  sisu-5.1.0.gem
* bin/sisu updated (modified to take account of gems)
* bin/sisugem added
* .gitignore sisu-*.gem sisu*.gemspec
  consider inclusion (& tracking) of rake created sisu4.gemspec sisu5.gemspec
  (as this makes their availability more obvious)
* once gem is installed: "sisu _5.1.0_ -vM" (to see version, commands otherwise
  as usual) if paths are such that sisu is not available "sisugem _5.1.0_ -vM"
  should work (as it is installed by gemspec, but not other sisu installers)

* do less by default
* remove rant generated sisu-install