PrimeFactors: Remove Wikipedia link.
t/PrimeFactors.t: Update tests.
PrimeFactors: Change colon to 'is'.
PrimeFactors: Change the wording of the result.

- If there are more than one factors say, "The prime factors of __ are __."
- If there is only one factor say, "The number __ is a prime."
PrimeFactor: 0 and 1 are not primes :smile:
PrimeFactors: Add additional triggers.

Add "factorization of n", "prime factorization of", and "prime factorization".
PrimeFactors: Reword to "$_ is a prime number."
PrimeFactors: Added new features:

- Use `factor_exp` instead of `factor`.
- Add commify to format the input.
- Add exponents to the primes. It's much easier to read.
Sum: Handle really big numbers.
Sum: Add a commify function.
Sum: Add a comment that explains the no bigint.
Sum: Fix tests.
PrimeFactors: Handle large integers.

- Enable bignum.
- Add alarm(1) to exit early if it's taking too long to compute (factoring is hard).
Merge pull request #371 from duckduckgo/jag/prime

Prime Factors: Review for Release
Merge pull request #377 from duckduckgo/jag/sum-improvements

SumOfNaturalNumers: Several improvements.