Bump version to 0.20
Remove the deprecated tools code
Remove ability to run our tests with atf-run

Kill all Atffiles and the support to run the tests with atf-run from
installcheck.
Remove --enable-tools and related code

Finally kill all traces of the deprecated tools by removing the flag that
controlled their build and assorted Makefile code related to it.
Remove obsolete configure code

This has been obsolted by the removal of the tools.
Redescribe ATF

ATF no longer ships a runtime engine, so make sure the introductory
description is accurate.
Release 0.19
Merge branch 'remove-tools'

This change removes the deprecated tools once and for all.  Any project
out there that may still need these should just import the standalone
'tools' subdirectory of atf-0.19 and use that instead.
Release 0.20