Update wellknown.md

apache config that would work for 1.3, 2.0, 2.2 and 2.4

This reverts commit 4dc99533.

I have no idea why I thought reusing the keys would be a good idea
when I first started this...

wellknown.md: Clarify WELLKNOWN variable

Keep registration information as json.

Use of 'grep -o' doesn't work on SunOS (fixes #164)

In some cases you need your registration id,
for example if you want to request a rate limit exception.
So keep the new-reg output on disk.