Makefile.am: Move tests into same directories as tested code

This allows for a cleaner build tree, and will provide benefits
when moving to a single Makefile.
configure.ac: Modernize the autoconf/automake invocation
Makefile.am: Use a single non-recursive Makefile

This allows all the code to be built in parallel, and only
rebuilding stuff that's changed when developing. Much quicker.

In the meantime disable the p11-tests checks, which
were very rarely used. We'll need to migrate them to TAP.
configure.ac: Put various autofoo litter in build/ an build/m4

Coverage also goes to build/coverage instead of testing/
Makefile.am: Don't do 'make distcheck' with silent make rules
Makefile.am: Use parallel tests for 'make check'

Also build in a 'make check-memory' and related functionality
which drives valgrind.