* Tempfile and temp directory cleanups
Add comments about mktemp on different platforms
Be more careful about tempfile cleanups
Don't use find to locate files to cleanup
Use shorter SECRETS_EXTENSION and SECRETS_DIR env settings in tests
Set TMPDIR in tests again
Show DESTDIR used when testing git-secret install
Change filename passed to mktemp -t in tests
* Only show 'cleaning up temp file' messages if one
of SECRETS_VERBOSE or SECRETS_TEST_VERBOSE is set.
* Adjust tests to reflect the change.
* Add note about suppressing 'cleaning up' msgs to CHANGELOG.md and reorder entries
* add comments showing examples of tmpfiles returned
