Add support for 'k', 'M', and 'G' suffixes to integer constants.

(Denoting units of 1024, 1024*1024, and 1024*1024*1024, respectively.)

Issue #128.

tests/kilo-mega-giga-2.ispc

@@ -0,0 +1,12 @@
+
+export uniform int width() { return programCount; }
+
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    int a = b + 2M;
+    RET[programIndex] = a;
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = 2*1024*1024 + 5;
+}