This converts the KWSys license to a pure 3-clause OSI-approved BSD
License.  We drop the previous license clause requiring modified
versions to be plainly marked.  We also update the KWSys copyright to
cover the full development time range.

STYLE: fix typo

Alex

ENH: Add support for multi-arguments: -f arg1 arg2 arg3 ... and support for lists: -f arg1 -f arg2 -f arg3 ... and for boolean to be stored as strings and doubles

ENH: Move callback structure out of the public interface. Also block the warning on Visual Studio Debug