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	Math for 2D rectangles defined as (x, y, w, h) where w > 0 and h > 0.
	Written by Cosmin Apreutesei. Public Domain.

DEFINITIONS

	A "1D segment" is defined as (x1, x2); a "side" is defined as (x1, x2, y)
	so it's a segment + an altitude. the corners are (x1, y1, x2, y2), where
	(x1, y1) is the top-left corner and (x2, y2) is the bottom-right corner.

PROCEDURAL API

	box2d.corners(x, y, w, h) -> x1, y1, x2, y2
	box2d.rect(x1, y1, x2, y2) -> x, y, w, h
	box2d.normalize(x, y, w, h) -> x, y, w, h
	box2d.align(w, h, halign, valign, bx, by, bw, bh) -> x, y, w, h
	box2d.vsplit(i, sh, x, y, w, h) -> x, y, w, h
	box2d.hsplit(i, sw, x, y, w, h) -> x, y, w, h
	box2d.nsplit(i, n, direction, x, y, w, h) -> x, y, w, h
	box2d.translate(dx, dy, x, y, w, h) -> x, y, w, h
	box2d.offset(d, x, y, w, h) -> x, y, w, h
	box2d.fit(w, h, bw, bh) -> w, h
	box2d.hit(x0, y0, x, y, w, h) -> t|f
	box2d.hit_edges(x0, y0, d, x, y, w, h) -> hit, left, top, right, bottom
	box2d.snap_edges(d, x, y, w, h, rectangles[, opaque]) -> x, y, w, h
	box2d.snap_pos(d, x, y, w, h, rectangles[, opaque]) -> x, y, w, h
	box2d.snapped_edges(d, x1, y1, w1, h1, x2, y2, w2, h2[, opaque]) -> snapped, left, top, right, bottom
	box2d.overlapping(x1, y1, w1, h1, x2, y2, w2, h2) -> t|f
	box2d.clip(x, y, w, h, x0, y0, w0, h0) -> x1, y1, w1, h1
	box2d.bounding_box(x1, y1, w1, h1, x2, y2, w2, h2) -> x, y, w, h
	box2d.scroll_to_view(x, y, w, h, pw, ph, sx, sy) -> sx, sy

OOP API

	box2d(x, y, w, h) -> box               create a new box object
	box.x, box.y, box.w, box.h             get box coordinates (for reading and writing)
	box:rect() -> x, y, w, h               get coordinates unpacked
	box() -> x, y, w, h                    get coordinates unpacked
	box:corners() -> x1, y1, x2, y2        left,top and right,bottom corners
	box:align(halign, valign, parent_box) -> box   align box
	box:vsplit(i, sh) -> box               split box vertically
	box:hsplit(i, sw) -> box               split box horizontally
	box:nsplit(i, n, direction) -> box     split box in equal parts
	box:translate(dx, dy) -> box           move box by (dx, dy)
	box:offset(d) -> box                   offset by d (outward if d is positive)
	box:fit(parent_box, halign, valign) -> box     enlarge/shrink-to-fit and align
	box:hit(x0, y0) -> t|f                 hit test
	box:hit_edges(x0, y0, d) -> hit, left, top, right, bottom   hit test for edges
	box:snap_edges(d, boxes) -> box        snap the edges to a list of boxes
	box:snap_pos(d, boxes) -> box          snap the position
	box:overlapping(box) -> t|f            overlapping test
	box:clip(box) -> box                   clip box to fit inside another box
	box:join(box)                          make box the bounding box of itself and another box

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See the source code for more info.