2.0 support

[H-Plus-Time]

With the imminent release of Polymer 2.0 (currently in Release Candidate), its probably time to consider porting over file-fire. I've forked the repository and begun work on that (I'll submit a PR by the end of the weekend), however I'd like to clarify what direction the maintainers would like to take in terms of the upgrade path (detailed in Polymer 2.0 Upgrade Guide). Either way, hybrid or class-based, the conversion doesn't take that long for single elements.

[sbeleidy]

I think initially we'd like to switch to hybrid and maybe later look at full polymer 2 support.

Thanks for taking this on!

[H-Plus-Time]

Oops, evidently Github doesn't allow for 'please add this branch to the base repo', that's actually what I meant :S.