Improved README and related.

* Updated explanation of features in README and a few other bits.
* README.txt is now the file to edit (in Pandoc format so people can
  actually read the table as text).
* To keep GitHub pretty, README.md is now generated based on README.txt.
* Updated makefile to generate above.
Reverted idiotic README idea.

* The "official" README is README.md again.
* Just treat the features table as a preformatted block of text.
* Reverted changes to makefile.
Merge branch 'dev/afbarnard' into dev/kboyd