Solve the problem 24 'Lexicographic permutations'.
nth_lexicographic_permution(): Convert to tail recursion to improve performance.
nth_lexicographic_permution(): 'divisor' is better name rather than 'stride'.
nth_lexicographic_permutation(): Reduce number of calls to number_of_permutations().
Solve the problem 25 '1000-digit-Fibonacci-number'.

Factor out common code of solutions of problem 13 and 25.
Solve the problem 26 'Reciprocal-cycles'.
26.Reciprocal-cycles: define a function returns the decimal representation of fractions.