Halberd THANKS file

Halberd has originally been written by Juan M. Bello Rivas.

Many people have further contributed to Halberd by reporting problems,
suggesting various improvements, or submitting actual code. Here is
a list of these people. Help me keep it complete and exempt of errors.

Dethy
Fabian Affolter
Sindre Pedersen Bjørdal
Andrés Riancho
