LibreJS support

[ChALkeR]

We should add LibreJS support, as documented in https://www.gnu.org/software/librejs/free-your-javascript.html

Our BSD-2-Clause License, taken from SPDX, is also known as FreeBSD License.

So we should label the code as being FreeBSD-licensed.

Ref: https://www.gnu.org/software/librejs/manual/html_node/Free-Licenses-Detection.html