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.
When printing a packet, dnstap-read checks whether its text form takes
up more than the 2048 bytes allocated for the output buffer by default.
If that is the case, the output buffer is automatically expanded, but
the truncated output is left in the buffer, resulting in malformed data
being printed. Clear the output buffer before expanding it to prevent
this issue from occurring.
