Implement Path#splitAt(offset)

Also make sure the deprecated Path#split(offset) works as it used to. Relates to paperjs#563

src/path/Path.js

@@ -1032,8 +1032,10 @@ var Path = PathItem.extend(/** @lends Path# */{
      * path.firstSegment.selected = true;
      */
     splitAt: function(location) {
-        var index = location && location.index,
-            time = location && location.time,
+        var loc = typeof location === 'number'
+                ? this.getLocationAt(location) : location,
+            index = loc && loc.index,
+            time = loc && loc.time,
             tMin = /*#=*/Numerical.CURVETIME_EPSILON,
             tMax = 1 - tMin;
         if (time >= tMax) {
@@ -1087,7 +1089,7 @@ var Path = PathItem.extend(/** @lends Path# */{
             location = time === undefined ? index
                 : (curve = this.getCurves()[index])
                     && curve.getLocationAtTime(time);
-        return location ? this.splitAt(location) : null;
+        return location != null ? this.splitAt(location) : null;
     },
 
     // DOCS: document Path#join(path) in more detail.

test/tests/Path.js

@@ -494,15 +494,16 @@ test('Curve list after removing a segment - 2', function() {
 
 test('Splitting a straight path should produce segments without handles', function() {
     var path1 = new Path.Line([0, 0], [50, 50]);
-    var path2 = path1.split(0, 0.5);
+    var path2 = path1.splitAt(path1.length / 2);
     equals(function() {
         return !path1.lastSegment.hasHandles() && !path2.firstSegment.hasHandles();
     }, true);
 });
 
 test('Splitting a path with one curve in the middle result in two paths of the same length with one curve each', function() {
     var path1 = new Path.Line([0, 0], [100, 100]);
-    var path2 = path1.split(path1.getLocationAt(path1.length / 2));
+    var loc = path1.getLocationAt(path1.length / 2);
+    var path2 = path1.splitAt(loc);
     equals(function() {
         return path1.curves.length;
     }, 1);