Handles scaling of input values to output values by using
a curve created from smoothly joining a number of set
control points.
This assists in creation of curve type transforms, typically
seen in raster image editing software (eg the curves dialog
in GIMP or Photoshop). Transforms are created by passing a
number of set control points through which the transform curve
must pass. The curve is guaranteed to exactly pass through
these control points. Between control points the curve is
smoothly interpolated so that no disjoint sections or
"corners" are present.
Remove QgsAbstractProperty and subclasses, and instead use a single
QgsProperty class which covers the use of QgsAbstractProperty
and its subclasses. This simplifies the API and avoids pointer
handling. QgsProperty is implicitly shared for memory efficiency
and inexpensive copies.
