add basic angle support (only used in calculation bounding boxes) to ASSLineTagSection:getMetrics(); also hook up angle support in ASSLineContents:getMetrics(), however it is currently not implemented for lines with more than one text section; add ASSClipVect:rotate() and ASSLineContents:getSectionCount() utility function; add basic support for "c" (close shape) drawing commands (not yet handled in ASSClipVect:getPositionAtLength/:getAngleAtLength)