obj_* function naming conventions


High level (new/destroy):

	This is the recommended way of creating new objects.

	pcb_*_new():
		Calls pcb_*_alloc(), fills in fields from parameters and calls the post
		processing (pcb_add_*_on_layer()) function as needed. Makes sanity checks
		on the parameters and may fail upon that. 

	pcb_*_new_*():
		Same as pcb_*_new(), but may do clever things so the object created may
		not be 1:1 what was requested or may not even be a new object (e.g.
		overlapping line merging)

	pcb_element_*_new():
		same as pcb_*_new(), parent being an element

	pcb_*_destroy()
		free all fields of an object and properly remove it from the parent
		(including rtree removal)

Low level (alloc/free):

	Use this in some special cases (like loading a file) when the extra checks
	of a _new may interfere. 

	pcb_*_alloc():
		allocate a new objects within a parent (as of now: layer). Allocates
		the struct of a new objects with all fields clean and links the object
		in the parent list. Returns a pointer to the object. NOTE: some post
		processing may be needed after filling in the fields
		(see also: pcb_add_*_on_layer())

	pcb_element_*_alloc():
		same, but parent is an element - will be removed once elements are
		generalized.

	pcb_*_free():
		free the struct memory (but not the fields!) of an object and remove
		it from the parent list.

	pcb_add_*_on_layer():
		Postprocessing: call this after a new object is allocated and fields are
		filled in. It mainly updates the rtree.

	pcb_*_copy():
		copy fields of a complex obj to a pre-allocated target obj


Accessors:
	pcb_*_get_*():
		Return data that are not directly accessible as object struct fields but
		require some sort of calculation

	pcb_*_set_*():
		Set object fields that require postprocessing because of side effects.
		Use these instead of direct writes to the fields to get side effects
		properly executed.

	pcb_*_change_*():
		Similar to pcb_*_set_*(), but instead of setting a field to a value
		specified as a parameter, change the field to comply with some global
		state, e.g. "change side" would move the object to the currently viewed
		side.

Transformations:
	pcb_*_move():
		move the object within its parent (x;y); it's often implemented as a
		macro

	pcb_*_mirror():
		mirror the object within its parent (x;y)


Misc:
	pcb_*_bbox():
		calculate and update the bounding box of an object

	pcb_*_rotate90()
		Rotate the object by n*90 degrees