Add Terraform (.tf) language support

[fourstepper]

I would like to add Terraform to the supported languages.

Creating this ticket for myself, will send a PR linked to this issue once this is ready.

[pokey]

Nice. I think terraform will be an interesting one. We might need to add some new scope types, but the large amount of repetition in terraform files should make for some cool multicursor operation once we've defined some good scope types