Update readme
New python sieve exercise adapted from ruby.
New python sum-of-multiples exercise
python matrix added.
Merge pull request #8 from sjakobi/matrix

python matrix added.
Merge pull request #7 from sjakobi/sum-of-multiples

New python sum-of-multiples exercise
New exercise: python series
Merge pull request #10 from sjakobi/series

New exercise: python series
New exercise: python octal
Merge pull request #9 from sjakobi/octal
New exercise: python difference-of-squares
Merge pull request #11 from sjakobi/difference-of-squares
Rename difference-of-squares example implementation
New exercise: python luhn
Merge pull request #13 from sjakobi/luhn

New exercise: python luhn
New exercise: python palindrome-products
Merge pull request #14 from sjakobi/palindrome-products

New exercise: python palindrome-products
New exercise: python nth-prime
Merge pull request #15 from sjakobi/nth-prime

New exercise: python nth-prime
New exercise: python largest-series-product