fix: change regex so it correctly identifies html encoded tags

[Hoverth]

Fixes #73.

I had to fiddle with the regex a bit, but it seems to be working.

I set the action for   to pop it, otherwise it results in the main equation bar being unreadable (see image below).

[Hoverth]

Hm, it was working before, but now it crashes the app upon there being a  .

[Hoverth]

Fixed by changing pop() to append("")

[Hoverth]

I've just added support for <, >, and & as html-encoded characters as well.

[jherkenhoff]

Thanks a lot for the contribution!

@all-contributors please add @Hoverth for code

[allcontributors[bot]]

@jherkenhoff

I've put up a pull request to add @Hoverth! :tada: