Support for more providers

[leonceaklin]

This fork adds a new dev command getproviders which runs a script that fetches oEmbed providers from the official oEmbed supported providers URL (https://oembed.com/providers.json) and stores them into endpoints-regexp.json with the same format like it was before.

As of October 9. 2020, there are 254 different providers which means that <o-embed> supports now two times more providers than before. The list gets updated constantly. Support for new providers are just a getproviders away.

Issue reference: #2