Added string to LargeInt conversion

Now we can have an array of Bytes in a string which will be converted to a LargeInt.
Simplification of the function Show.
Add algorithms and Build Type choice.

Now you can choose with cmake the Build Type : Release or Debug.
Many algorithms had been included :
- A number generator
- The Fermat Primality test
- The Euclide Algorithm to find PGCD
- And the probabilistic Miller-Rabin Primality test
Example program added and Algorithms working

Now you can choose to compile the example test program of the library.
The Algorithms are now usable.