Add .htmlnanorc support

[Kirill Maltsev]

For storing configuration.

[Sukka]

Instead of .htmlnanorc, I prefer the following formats:

• .htmlnanorc.cjs
• .htmlnanorc.js
• .htmlnanorc.yaml
• .htmlnanorc.yml
• .htmlnanorc.jsonc
• .htmlnanorc.json

I'd like to port the feature from mochajs:

https://github.com/mochajs/mocha/blob/1a4646dd2f7b35010c2488edcb2d5f4cfb2f14a8/lib/cli/config.js

[Brennan Kinney]

You can use CosmicConfig as a popular approach for pulling config from a file which supports various formats.

[Kirill Maltsev]

Implemented in 2c03b10 (forgot to add the issue number there).