Add new method to API allowing users to define their own eq. percentage.

- Move DEFAULT_DEFINITION_OF_EQUAL into the interface.
- Add new method compare(BufferedImage, BufferedImage, double) to interface
  and first processor implementation.
- Add new private variable to implementation: myDefinitionOfEqual.
- The "old" method compare(BufferedImage, BufferedImage) calls the new method
  now and uses the default value from the interface.
Set project name explicitly.
Fix Jar not having a version number.
Clean the version number when running 'release' target.