Added pv_where and asConstraint implementation + switched to PVConstraintContext
Added PVVFL initial builder
added PVLeftOf() function
working on relation part
done relation part
completed single constraint with tests
removed old code
Merge pull request #9 from DAlOG/vfr_support

Single constraint feature
Separated single constraint layout to locationional and size.
Merge pull request #10 from DAlOG/develop

Completed single constraint feature.