New static methods for creating Bezier curves

[stribor14]

• fit to polyline
  • fits a bezier curve of order N that passes through N dominant points on polyline and minimizes RMSD (root mean square dstance) and length difference (compared to given polyline)
• join curves
  • fits a bezier curve through concatinated polyline representations of given curves
• curve offset
  • fits a bezier curve through points computed as polyline representation offseted by some distance in direction of normal vector

close #37 #43
Some work done towards #41

[stribor14]

@kturkovic you don't have to check fromPolyline method in detail, because it is refactored already on the other branch to be more efficient and stable, but that branch depends on some new functionalities that break current library interface