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

Issue #139.

tests/new-delete-5.ispc

@@ -0,0 +1,17 @@
+
+export uniform int width() { return programCount; }
+
+struct Point {
+    uniform float x, y, z;
+};
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    float a = aFOO[programIndex]; 
+    varying Point * uniform buf = uniform new varying Point(a, b, 1234.);
+    RET[programIndex] = buf->y;
+    delete buf;
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = 5;
+}