Pass 'cache' as a keyword argument to the wrapper

This makes 'cache' acessible via __kwdefaults__
Add a solution to the problem 92
Optimize the sum_squares function
Optimize the solution

Process numbers n <= 9^2*7 and calculate how many numbers below 10^7
have the sum of the squares of their digits equal to n
Optimize the solution

Compute the sums frequencies iteratively, using the frequencies for the
previous number of digits.