This commit converts the license handling to adhere to the REUSE
specification. It specifically:
1. Adds used licnses to LICENSES/ directory
2. Add "isc" template for adding the copyright boilerplate
3. Changes all source files to include copyright and SPDX license
header, this includes all the C sources, documentation, zone files,
configuration files. There are notes in the doc/dev/copyrights file
on how to add correct headers to the new files.
4. Handle the rest that can't be modified via .reuse/dep5 file. The
binary (or otherwise unmodifiable) files could have license places
next to them in <foo>.license file, but this would lead to cluttered
repository and most of the files handled in the .reuse/dep5 file are
system test files.
- this required modification to the code that generates grammar text for
the documentation, because the "dnssec-lookaside" option spanned more
than one line in doc/misc/options, so grepping out only the lines
marked "// obsolete" didn't remove the whole option. this commit adds
an option to cfg_test to print named.conf clauses only if they don't
have the obsolete, ancient, test-only, or not-yet-implemented flags
set.
