specs: propagate package.path to specl subprocesses.

* specs/specl_spec.yaml (specl.before::run_spec): Add the package.
path to forked specl command so that it has access to ansicolors
et.al. from the parent LUA_PATH, which may have been carefully set
to match the interpreter by the caller.
* specs/formatters_spec.yaml (formatters.before::run_spec): Ditto.
Also, escape single quotes in yaml before passing to printf.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>