add math utils; integrate checked expression macros

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/utils/mod.rs

@@ -5,6 +5,7 @@ pub mod defer;
 pub mod hash;
 pub mod html;
 pub mod json;
+pub mod math;
 pub mod mutex_map;
 pub mod rand;
 pub mod string;