WTFPL(-2.0) license entry

Jan Engelhardt <jengelh@...>

The SPDX license list at has an entry

Do What The F*ck You Want To Public License WTFPL

There are multiple versions of the WTFPL around, and the SPDX entry
shows the WTFPL version 2.0 text. In spirit of the SPDX naming of all
the remaining licenses, the "WTFPL" entry should be renamed to