Parse a slice of strings (representing integers in decimal)
Convention: this function is to be applied to strings representing Q.128 fixed-point numbers, and thus returns numbers in binary Q.128 representation
polyval evaluates a polynomial given by coefficients `p` in Q.128 format
at point `x` in Q.128 format. Output is in Q.128.
Coefficients should be ordered from the highest order coefficient to the lowest.