Improve performance

[Zomis]

Improve performance. Things that might require refactoring is GroupValues and FieldGroup. GroupValues uses the non-primitive Integer for example, while a good old int would suffice.

[Zomis]

GroupValues could possibly use an byte[], where each field is an index in the array. Something like:

• 0 = unset
• 1 = field has value 1
• -1 = field has value 0

All that is needed then is for a good way of connecting a field to an integer. In worst case, this can be done with Map<T, Integer> but I hope for another solution. Perhaps create some Wrapped<T> with the T and an int.