update gem2arch to follow PKGBUILD-rubygem.proto

Hi,

as gem2arch doesn't follow the Ruby Guidelines of Arch and the PKGBUILD-rubygem.proto anymore I've modified the python code to fix that.


Regards,
Andrwe

------ Commit-Message
- directories created by gem2arch follow ruby guidelines (ruby-$_gemname)
- the PKGBUILD created by gem2arch define $_gemname
- all calls of '% (gem_spec.name)' are replaced by $_gemname

Signed-off-by: Andrwe Lord Weber <github@andrwe.org>