Added get_height() and no_children() to common.scad.

Changed the epsilon in one of offset's subfunctions from 1e-4 to
1e-6.
Modified rounded_sweep() to take h, l, or height, and to have default
behavior if height is omitted.  It also quantizes the path to 1/1024.
Added no_children check to module offset_stroke().

geometry.scad

@@ -1026,7 +1026,7 @@ function _good_segments(path, d, shiftsegs, closed, quality) =
 	) [
 		for (i=[0:len(shiftsegs)-1])
 			(i>maxind)? true :
-			_segment_good(path,pathseg_unit,pathseg_len, d - 1e-4, shiftsegs[i], alpha)
+			_segment_good(path,pathseg_unit,pathseg_len, d - 1e-7, shiftsegs[i], alpha)
 	];