added Nitpick's theory and ML files to Isabelle/HOL;
the examples and the documentation are on their way.
header {* Main HOL *}theory Mainimports Plain Nitpick Quickcheck Recdefbegintext {* Classical Higher-order Logic -- only ``Main'', excluding real and complex numbers etc.*}text {* See further \cite{Nipkow-et-al:2002:tutorial} *}end