README.md is now README.adoc

Conversion done automatically via:
kramdoc --format=GFM --output=README.adoc --wrap=ventilate README.md

The ventilate option put one sentence per line.
A personal preference of mine, as per:
https://asciidoctor.org/docs/asciidoc-recommended-practices/#one-sentence-per-line
but something I'll try not to be pedantic about.

Some minor touch ups after conversion:
- The README.md typically made use of variables for urls.
Since it was easy for me to follow suit in adoc, I did.
Seems like a good idea.
- Fixed circleci badge.

Closes clj-commons#396