multiMap() function - integer linear interpolation

Thanks for sharing!

I think it is a great example what can be done with templates, but I agree with PaulS that using different types for all parameters is overkill for 99.9% of all sketches I have seen.

If a user wants performance (s)he inlines the formula
If a user wants precision (s)he either selects float (because it rounds better in the division) or uses long.