Problem:
The "tohtml" plugin is loaded by default.
Solution:
- Move it to `pack/dist/opt/nvim.tohtml/`, it is an "opt-in" plugin now.
- Document guidelines.
- Also revert the `plugin/` locations of `spellfile.lua` and `net.lua`.
That idea was not worth the trouble, it will be too much re-education
for too little gain.
