Licensing overhaul

[jpellegrini]

HI,

@egallesio since you mentioned in issue #118 that GFDL would be OK I added a copy of it.

I'm not sure if this is good, but since there is code licenses and documentation license, I modified COPYING to only mention authorship and license, referring to the license files from there.
The diff shows a change in the GPL-2 file, but that is only because I put a standard copy of it, and git recorded it as a modification to COPYING.

I'm not sure you agree -- this is really only a proposal!

(Identifying the licenses of some files, as mentioned in issue #119 would still be pending, but this PR would perhaps be good anyway?)

The changes:

• Only mention copyright in COPYING, referring to the license files
  from there. Also mention that some files have different license and
  authors.

• ADD GPL-2 and GFDL-1.3.

• Mention copyright in README.md.

[lassik]

The https://reuse.software/spec/ specification recommends a LICENSES/ directory in the repo, with the license files named like:

• LICENSES/GPL-2.0-or-later.txt
• LICENSES/GFDL-1.3-or-later.txt

@weinholt is using this layout in the Scheme package manager Akku. Do Debian tools support this?

[weinholt]

@lassik Are you asking me? I don't know what such support would look like, but maybe one of the tools at https://wiki.debian.org/CopyrightReviewTools does something special with it. We usually try to figure out upstream's licenses ourselves, which is always a manual job (though possibly supported by tools). Sometimes it can be like detective work, but upstream is rarely directly involved.

[jpellegrini]

@egallesio is it OK for you to have a LICENSES/ directory, as @lassik mentioned?

Anyway -- if a file was adapted, then it would be, for example, "orginally MIT with GPL modifications by Erick Gallesio", for example. It should not be considered as an MIT-licensed file, but rather GPL, as I understand. However, the text of the MIT license should stay there, because it is the original license, and was "sublicensed" as GPL.
So I suppose it would be nice to have the text of all licenses in that directory, and have the top-level COPYING file explain that the whole thing was relicensed as GPL. Is this reasonable?

[egallesio]

@egallesio is it OK for you to have a LICENSES/ directory, as @lassik mentioned?

Yes, this is the best way to avoid cluttering the main directory.

So I suppose it would be nice to have the text of all licenses in that directory, and have the top-level COPYING file explain that the whole thing was relicensed as GPL. Is this reasonable?

I'm not a lawyer, but it seems OK for me.

[lassik]

SPDX is an organization that is trying to standardize how license information is marked in open source projects, and their conventions are now being used by the Linux kernel et.al. The information is marked in a source code comment at the top of each file. Here is the explanation from Linux. What do you think about using these SPDX-License-Identifier: comments in the STklos source?

[lassik]

The more complex comments would look something like this: /* SPDX-License-Identifier: MIT AND GPL-2.0-or-later */

Each well-known license is referred to using a standard identifier; here is the list of them all.

[lassik]

Some projects are developing tools to auto-extract these comments to figure out the license of a project, including the above REUSE initiative.

[jpellegrini]

@egallesio -- I remember some of my adaptations of SRFIs were released under GPLv3-or-later. Now I realize one thing: if I understand correctly, that means any redistribution of STklos with them would also need to be GPLv3-or-later, so if you want, I may change those to GPLv2-or-later (the same as STklos currently).
Or if you want to change the whole code base to GPLv3-or-later, I'll be happy too :) -- it's your choice of course!

[jpellegrini]

Also -- @egallesio -- what do you think of @lassik 's idea? Can we add SPDX headers to the source files? I can make a PR if it's OK with you.