Add ruby plugin

[cmatsuoka]

Port ruby plugin from Snapcraft PR: canonical/snapcraft#3511

Plugin needs to be reworked to validate an existing ruby interpreter or to use an interpreter built in a different part.

[paddor]

I've cloned craft-parts and created and registered the RubyPlugin. How do I test whether it works as a part in my app?

[paddor]

Using env PYTHONPATH=dev/oss/craft-parts/ python3 -mcraft_parts I can make it load the local repo of craft parts. But how do I use it with the snapcraft command?

[postmodern]

Any update on this? I'm struggling to create a snapcraft with certain gems pre-installed. The documentation for using the ruby plugin references core18, although core20 might work as a fallback?

[paddor]

Any update on this? I'm struggling to create a snapcraft with certain gems pre-installed. The documentation for using the ruby plugin references core18, although core20 might work as a fallback?

I have a working Ruby plugin for core20 I think. But it doesn't use craft-parts if I remember correctly. I can put it in a gist tomorrow.