new: LiquidOptions.dateFormat to override default date format

[prassie]

doc: updates related to LiquidOptions.dateFormat
doc: revamped the date filter doc for easier reference

const liquidjs = require("liquidjs");
console.log(new liquidjs.Liquid({ dateFormat: '%d%q of %b %Y at %I:%M %P %z'})
                        .parseAndRenderSync(`{{ '1990-12-31T23:30:28Z' | date: undefined, -330 }}`));

=> 01st of Jan 1991 at 05:00 am +0530

Can be used as a workaround for #567, though the date format flags need to be strftime compatible.

[harttle]

Thanks @prassie for updating the docs, it's surely outdated since the source code changed a lot, it indeed looks better, thank you!

[github-actions]

🎉 This PR is included in version 10.6.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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