Changing licensing to dual-license MIT and Apache 2.0.

It's not really possible to write a programming language using strong
copyleft licenses (I'm not aware of any that do). My motivation for
using LGPL was to protect the Trifle source code itself. However, the
LGPL discusses 'linking', which makes less sense for a scripting
language. I want to be unambiguous that you can release a Trifle program
under any license without problem.

This would mean the MIT licence is sufficient. However, including the
Apache licence gives us some patent protection, which is worthwhile.

I would encourage users to use GPL for their own software, but
ultimately it is their choice.