Changes: streamlined entry/main function.
Note: Due to GMP compatibility issues with Windows, 10^8 digits is the most it can calculate.
Now allows inputting the number of digits to calculate.
Benchmarks:
(Run on Intel Core i5 8300H)
Also, on an Intel Core i7-1185G7, the time for calculating 100 million (10^8) digits was 66.9916 seconds.