svg output point-symbol=line and -style rotate=

[cedricsam]

• added support for drawing a line as a point-symbol= on svg output
• added support to rotate a point symbol using data
  • could clash with desired software design, by adding an attribute on the point feature called rotate=... I did it that way, because I wanted to be able to use expressions and layer data to provide an arbitrary rotation based on data. The immediate desire was to let people use an r= that remains a radius, which has to be positive and generally the Math.sqrt() of a numeric value we want to represent.
• the line starts at the feature's specified point, and goes in the direction of the rotation
• refactored the square point-symbol
  • now a polygon instead of a rect, so that it can be rotated without having to use transform() and much weirdness in the maths (since the origin isn't the point itself, but the whole svg).
  • instead, we use Math.cos() and Math.sin() to translate the coordinates of the four vertices
  • the square is actually "standing up" and we apply a 45-degree rotation by default to make the square with its side perpendicular and parallel with the canvas'.
• tried outputting a test SVG using U.S. counties and some data in the MY_DATA_FIELD column:
  • test -style command is: -style r='Math.sqrt(Math.abs(MY_DATA_FIELD))' rotate='MY_DATA_FIELD >= 0 ? -90 : 90' stroke='COLOR' opacity='.5' fill='none' target=POINTS_LAYER
  • try with point-symbol=line in the -output command
  • in Illustrator, I was able to select lines and apply an a arrow style (the right side arrow in the Illustrator stroke dialog was applied on the side of the x2, y2 point, so pointing away from the point's center)
• there was a previous iteration of this that worked where I had point-symbol-rotate= (and a numeric degree value as argument) in -output, but I couldn't find how to evaluate expressions...

[cedricsam]

Was resubmitted to branch out from 0.4.105