Introduce doNotParse callback setting to allow for implimenters to bypass notes.

[peterwilsoncc]

The WordPress version of Twemoji has been modified to introduce a doNotParse callback to be included in the settings to indicate that a node should not be parsed.

For WordPress, contributors use this to bypass any node that includes the class wp-exclude-emoji. For context, see the WordPress ticket #52219.

Would it be possible to introduce the use of the custom callback to Twemoji Core?

For WordPress, we make use of the callback in parse() and grabAllTextNodes() but I am happy to provide a PR if you are willing to consider the setting as suitable for the Twemoji library.