greatly simplify overlap detection

Exploits the knowledge that w and h are non-negative.

All it took was a question on the LÖVE Discord, which pointed me at the
technical term of AABB (axis-aligned bounding box) collision detection.

0117-straddles_interval

@@ -1,3 +0,0 @@
-straddles_interval = function(lo,hi, border)
-	return lo <= border and hi >= border
-end

0118-overlapping_intervals

@@ -1,6 +0,0 @@
-overlapping_intervals = function(alo,ahi, blo,bhi)
-	return straddles_interval(alo,ahi, blo)
-		or straddles_interval(alo,ahi, bhi)
-		or straddles_interval(blo, bhi, alo)
-		or straddles_interval(blo, bhi, ahi)
-end

0119-overlapping_areas

@@ -1,5 +1,5 @@
 -- return true if a is less than some distance from b
 overlapping_areas = function(a, b)
-	return overlapping_intervals(a.x, a.x+a.w, b.x-20, b.x+b.w+20)
-		and overlapping_intervals(a.y, a.y+a.h, b.y-20, b.y+b.h+60)  -- leave more space below existing definitions
+	return a.x < b.x + b.w+20 and a.x + a.w > b.x-20
+		and a.y < b.y + b.h+60 and a.y + a.h > b.y-20
 end

0127-test_straddles_interval

@@ -1,3 +0,0 @@
-test_straddles_interval = function()
-	check(straddles_interval(-20, 21, 0), '1')
-end

0128-test_overlapping_intervals

@@ -1,3 +0,0 @@
-test_overlapping_intervals = function()
-	check(overlapping_intervals(0, 1, -20, 21), 'within')
-end