* test/assess-test.el: Assume `cl-lib` is available.  Silence warnings.
(strings-with-unequal-properties): Use `font-lock-ensure` when available.

* test/assess-call-test.el (assess-call-test-capture-fail)
(assess-call-test-hook-fail): Silence compiler warnings.

* dev-resources/elisp-unindented.eld:
* dev-resources/elisp-indented.eld: Change extension from `.el`.

* test/local-sandbox.el:
* test/assess-discover-test.el:
* dev-resources/elisp-fontified.el: Enable lexical-binding.
Add copyright notice.

* assess-discover.el:
* assess-call.el: Adjust copyright.

* assess-robot.el: Adjust copyright.  Silence compiler warnings.
(assess-robot-copy-and-finish): Simplify a tiny bit.

* assess.el: Adjust copyright.  Assume `advice-add` is available.
(assess--face-at=-1, assess--file-face-at=-1): Use `font-lock-ensure`
when available.

* .gitignore: Add ELPA-generated file.