Implement the REUSE specification for licensing and copyright

Implement the REUSE specification for licensing and copyright

See "https://reuse.software/tutorial/", running the linter now returns
this :

$ reuse lint

* Bad licenses:
* Deprecated licenses:
* Licenses without file extension:
* Missing licenses:
* Unused licenses:
* Used licenses: BSD-2-Clause, FSFAP, GPL-2.0-or-later, GPL-3.0-or-later, LicenseRef-Autoconf-exception-macro, Linux-man-pages-copyleft, Linux-syscall-note, MIT
* Read errors: 0
* Files with copyright information: 52 / 52
* Files with license information: 52 / 52

Congratulations! Your project is compliant with version 3.0 of the REUSE Specification :-)

Change-Id: Ifa9f7bc1cbdce204dd8bad4b8978d90b0d7bb90a
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>