Refactored to use interface Map.Entry instead of the implementation SimpleEntry
fixing probability calculation
Moved mappers to a different package.

Issue #135
Refactored comparators by moving them into a seperate package and exposing them
via enum in interface

Issue: #134.
Files modified. Issue: #134
Deleted extractor interface
Deleted unwanted imports
Merge branch 'unstable' of https://github.com/b0noI/AIF2 into unstable
Refactored
refactoring stemmer
adding functional test