Add darix' version as starting point
Adapt preamble to changes from darix
Use gem2rpm to handle doc install options
Update %post contents to our latest
Typo
Integrate darix' changelog
Use gem2rpm with YAML config support

This is instead of our customised template.  The custom stuff is now in
the generic sles12 template, and the things we change are defined
statically in gem2rpm.yml.