Presslyte browser assets

All original, readable JavaScript and CSS source files are included beside
their .min.js and .min.css production files in assets/. No external service
or build tool is required to run the installed plugin.

To reproduce the production assets with Node.js:
  npm install --no-save terser@5.44.1 clean-css@5.3.3
  node tools/build-assets.js

Run those commands from a development copy of this plugin. Do not include
node_modules in the distributed plugin. Terser performs local-variable
minification without property-name mangling. CleanCSS uses level 1 only,
with URL rebasing disabled; rule order and asset paths are preserved.

Plugin source and generated assets: GPL-2.0-or-later.
