feat: Add Multiply-add function to compute x*y+z

[danielelli]

Info

This PR adds a similar function method of C++'s fma cmath function.

What has been added is:

• fma(x,y,z): computes and returns the result of x * y + z without losing precision of any intermediate results.

Example:

let x = 15.0
let y = 16.0
let z = 17.0
fma(x, y, z) // 257.0

• test cases for fma() have been added to the test folder in it's own file.

[korbexmachina]

Everything seems to be in order, thank you for adding a useful macro and submitting a pull request!

[korbexmachina]

Note: This should be published in the next minor version. (v0.2.0)