libdocument: adding method is_xy_in_annotation

Added the method is_xy_in_annotation to the
interface of document-annotations. It intends to
check if a point (x,y) is inside the annotation's
quadrilaterals (and not its bounding box, which
can be checked using the EvMapping).
pdf: implemented is_xy_in_annotation

Implements the function that checks whether a point
(x,y) is inside an annotation.