Add support for ES6 modules

Export the default TextObserver class so you can actually use them in your own separate file...

Multiple observers, manual control, and fixes galore

A ton of improvements have been made since the first release, enough that I've given this a new major version number.

The headline features are support for multiple TextObserver instances and manual disconnect() and reconnect() methods. TextObserver now covers a much wider range of cases, including:

• Special HTML attributes that get rendered as text (placeholder for <input>, alt text, etc.)
• CSS content property
• Shadow DOMs

In addition, mitigations have been applied so that pages are now much less likely to slow down or crash on "recursive" replacements, like "expands" to "physically expands."

Initial release

1.0.0

Initial commit