Implement basic integer math operations

HELP.md

@@ -319,6 +319,29 @@ Append the given `value` to the current destructured.
 Example: `[foo, bar]` -> `push foo` -> `[foo, bar, foo]`
 
 
+### Numeric Operations
+
+#### `plus <val>`
+Add `val` to the current subject.
+Example: `4` -> `add 3` -> `7`
+
+#### `minus <val>`
+Subtract `val` from the current subject.
+Example: `4` -> `sub 7` -> `-3`
+
+#### `abs`
+Take the absolute value of the current subject.
+Example: `-3` -> `abs` -> `3`
+
+#### `times <val>`
+Multiply the current subject by `val`.
+Example: `3` -> `times 4` -> `12`
+
+#### `divide <val>`
+Divide the current subject by `val`.
+Example: `12` -> `divide 3` -> `4`
+
+
 ### Working with Variables
 
 Variables in `str` start with a dollar sign and may be alphanumeric with underscores (e.g. `$my_var`).