Move tests/run-test-suite to branch run-test-suite

with the intent that `make test-suite` will use it as a branch.

This commit makes the libyaml and yaml-test-suite repos completely
independent. The only thing in master is a Makefile rule for
`make run-test-suite`.

The run-test-suite branch takes care of everything else.

This will keep the master branch history clean from any yaml-test-suite
activity, while keeping everything up to date.

Pinning will just work for whatever commit of master you run the tests
from. The pinning work will all be done in the `run-test-suite` branch.