Add support for "new" and "delete" to the language.

Issue #139.

tests/new-delete-6.ispc

@@ -0,0 +1,17 @@
+
+export uniform int width() { return programCount; }
+
+struct Point {
+    float x, y, z;
+};
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    float a = aFOO[programIndex]; 
+    Point * varying buf = new Point(0., b, a);
+    RET[programIndex] = buf->z;
+    delete buf;
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = 1+programIndex;
+}