REQUEST: Assign Syntax-Highlichter via RegExp

[micha_he]

Instead of assign the Syntax-Highlighter via file-extension, expand it to a regular expression.

This allows, that we assign a file like "rules\d\.txt" or "rules[1-4]\.txt" to a special rules-highlighter (in this example rules for EspEasy IoT) and not to the default for txt-files.