Structured metadata file for each episode

To keep this repo as the (kind of) single source of truth, and to aid in API building, I think it would be a good idea to keep some structured metadata file per episode. I would propose the YAML format for its human-and-machine-friendliness.

The most important information that I'd like to see there is the publication date and original language. Those are hard to find out otherwise.

This allows, for example, the episodes.json to exclude episodes that have no publication date or a publication date in the future.

---

If we're at it, why not also add:

• Number of financial supporters
• Credits (co-scenarists, proofreaders, script doctors, worldbuilders, software, etc.)

…so that this doesn't have to be scraped from the SVGs.

@ctk and I have build a title scraper that's doing a pretty good job by now, so the titles don't have to be repeated, but they could be (automatically).

---

What would be nice to have as information too, is the translators per episode, but I guess this was dropped because it was a hassle to maintain. We could try our hand at a "translator extractor scraper", maybe that could work.

---

So for example:

ep25_There-are-no-Shortcuts/info.yaml

---
# Leave publication date empty until episode is released
# Strictly use format YYYY-MM-DD
published: 2018-05-17

# Two-letter "P&C language code" of the language the comic was first created in
original_language: en

# Leave financial_supporters empty until number is known
# Fill in an integer, and only an integer
financial_supporters: 909

credits:
  - name: David Revoy
    role: [art & scenario, universe creator]
  - name: Nicolas Artance
    role: beta feedback
  - name: Imsesaok
    role: beta feedback
  - name: Craig Maloney
    role: [beta feedback, universe contributor]
  - name: Valvin
    role: beta feedback
  ⋮

software:
  - name: Krita
    version: 4.0.0
  - name: Inkscape
    version: 0.92.3
  - name: Kubuntu
    version: 17.10