Stop using `about`, `description`, `address` tags

[fiatjaf]

It's better to just have the same information in a canonical place, saving everybody the hurdle of transmitting the repeated data over and over, and then checking all possible locations.

Since Flockstr is the only client doing these events for now as far as I know, whatever it does will be the actual standard, so if Flockstr checks for "description" data in 3 different places the standard becomes "description can be in any of these places" -- then in the future other apps will each put the description in one of these places, which forces all apps to check all places, but just to be sure apps will opt to publish the data in all of these places forever, which means events will be unnecessarily big forever.

The same applies to "address" and "location".

I am not sure my changes here are fully correct, but I can improve them if you agree with the changes.

Also I recommend following the same approach for other events that Flockstr is generating, the subscription stuff, for example. But I didn't change these since I don't know what is the preferred way. I suggest that you pick one standard and be strict about it. Thank you!