docs: add docsify site

[dnlup]

Fixes #232

• setup docsify
• setup publishing branch
• decide deployment strategy (SSR vs GH pages)
• setup ci

[codecov]

Codecov Report

Merging #262 (8699e1a) into next (2d78dc9) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              next      #262   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           12        12           
  Lines          286       286           
=========================================
  Hits           286       286           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2d78dc9...8699e1a. Read the comment docs.

[dnlup]

After some experimenting, it turns out that SSR is not well supported in docsify atm, leaving GH pages as the remaining option.

At least until docsifyjs/docsify#1227 is merged.