Function to calculate the cumulative probability corresponding to a given a z value from a normal distribution.
The user input is as follows:
z value: A number that can be from - infinity to + infinity. E.g. -1.65
The cumulative probability from the left tail of the distribution till the given z value.
S Subramanian <email@example.com>
John C. Hull, "Options, Futures, and Other Derivatives", 8/E, Prentice Hall, 2012.