copy subset of Sprig template functions

docs/sprig/math.md

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+# Integer Math Functions
+
+The following math functions operate on `int64` values.
+
+## add
+
+Sum numbers with `add`. Accepts two or more inputs.
+
+```
+add 1 2 3
+```
+
+## add1
+
+To increment by 1, use `add1`
+
+## sub
+
+To subtract, use `sub`
+
+## div
+
+Perform integer division with `div`
+
+## mod
+
+Modulo with `mod`
+
+## mul
+
+Multiply with `mul`. Accepts two or more inputs.
+
+```
+mul 1 2 3
+```
+
+## max
+
+Return the largest of a series of integers:
+
+This will return `3`:
+
+```
+max 1 2 3
+```
+
+## min
+
+Return the smallest of a series of integers.
+
+`min 1 2 3` will return `1`
+
+## floor
+
+Returns the greatest float value less than or equal to input value
+
+`floor 123.9999` will return `123.0`
+
+## ceil
+
+Returns the greatest float value greater than or equal to input value
+
+`ceil 123.001` will return `124.0`
+
+## round
+
+Returns a float value with the remainder rounded to the given number to digits after the decimal point.
+
+`round 123.555555 3` will return `123.556`
+
+## randInt
+Returns a random integer value from min (inclusive) to max (exclusive).
+
+```
+randInt 12 30
+```
+
+The above will produce a random number in the range [12,30].