Simplify LICENSE wording

Simplify LICENSE wording

Now, before you call your lawyers, here is some explanation:
The MIT/X Consortium-License and ISC-License are equivalent
according to the Berne-convention. This means that a court
of law presented with either licenses will act the same.

The advantage of the ISC license is that it has a simpler wording
and is recommended by the OpenBSD-project for new projects[0].
And as we at suckless.org love removing cruft, this also includes
removing legal cruft wording that is not needed any more.

[0]: http://www.openbsd.org/policy.html