Klever

In a nutshell there are 2 comparison functions that one can select when creating unsafe marks. These functions compare results of work of 2 other functions strictly bound with them and associate marks with unsafes according to a degree of similarity. Sometimes users need some special functions that may be more or less common (obviously generally useful stuff should be committed to the Klever repository). I suggest to describe how to support new functions for unsafe marks so that everybody will be able to do that themselves at an appropriate time.