Added DistanceFunction interface
Added another norm method
Euclidean distance function has been implemented
Manhattan distance function has been implemented
Added basic implementation of Maximum distance function
Abstract vector implementations now override extended norm method
norm() method has been refactored
Added comment
Fixed bug related with delegation method call
Renamed file DistanceFunction to NormFunction
Renamed public class to NormFunction
Done some refactoring related with renaming DistanceFunction to NormFunction
Changed norm's implementation names
Fixed type error
Moved NormFunction interface to Vectors class
Done some refactoring
Merge pull request #138 from maseev/iss135

Fixes #135
added credits for Miron