Fix typo, documentation link changed to point to jqueryvalidation.org instead of validation.bassistance.de

This does 2 things:

1.  Fixes a typo in the maxlength-method documentation
2.  Changes the documentation link in the root of the site to point to http://jqueryvalidation.org/documentation/ instead of http://validation.bassistance.de/documentation/ (by the way the same result could equally be achieved by turning the link into a relative link instead of a fully qualified one)