YarnFlow on needle is now a set instead of a list.
Knitted2 now auto-tracks the yarns, just needes the stitches.
Simplify knitting impl as a preparation to other kinds of knitting.
Fix test (set instead of list).
implement MC-knitting.
Code cleanup.
Remove redundand yarn from yarn flow and improve to toString.
Better error message.
Return yarn attachment from knitting carriage.
Only track the yarn position in the attachment and no longer everywhere (there only YarnStart is used).
Performance optimization.
Rename YarnStart to YarnPiece.