- switch requires of the autogenerated subpackages from
rb_suffix-rubygem-gemname = version to
rubygem(rb_abi:gemname) = version

- split our the rails part

- we need bundler now. given ruby 2.5 will have it intree anyway,
this soon wont be a big burden.

- add support to generate requires from Gemfile.lock

- package the buildinfo dir
- allow passing options to extconf.rb