typo: first "describe" in shell_spec.yaml should be "describe shell".

* specs/shell_spec.yaml (describe specl): Rename from this...
(describe shell): ...to this.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
typo: spell the matchers module name correctly in documentation.

* docs/specl.md (Custom Matchers): The module is called `matchers`
not `matcher`, and API calls are now fully qualified.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
specl: remove implicit imports misfeature.

* src/specl.lua (initenv): No need to clobber the environment
with everything in the table returned from any `require` in a
spec file.
* specs/shell_spec.yaml, specs/optparse_spec.yaml: Explicity
import function symbols from `specl.shell` as needed.
* NEWS: Update.

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