Although the addition of "version 3 or later" to the README [1] predates the
commit that added LICENSE.txt with the description "LGPLv3 for code" [2]
I think it's safe to go with the latter since the terms were clarified
again by the original author explicitly without the "or later" clause [3].
closes#575
[1]: May 2013 8be0d0e1d975ef93b38918f19b36b58b5c873b07
[2]: Sep 2013 c3082f660175bdeb6205f19418f0bf8b43ba10f6
[3]: May 2016 85bc62a65d05c6e6066fba12b6551364561ab207
