ruby/all-your-base: add solution
ruby/binary-search-tree: add solution
ruby/isbn-verifier: add iteration
ruby/nth-prime: add solution
ruby/armstrong-numbers: add iteration
ruby/atbash-cipher: add iteration
ruby/binary-search: add iteration
ruby/circular-buffer: add iteration
ruby/flatten-array: add iteration
ruby/gigasecond: add iteration
ruby/grade-school: add iteration
ruby/high-scores: add iteration
ruby/largest-series-product: add iteration
ruby/linked-list: add iteration
ruby/list-ops: add iteration
ruby/difference-of-squares: add iteration
ruby/nucleotide-count: add iteration
ruby/pangram: add iteration
ruby/raindrops: add iteration
ruby/prime-factors: add iteration
ruby/sum-of-multiples: add iteration
ruby/perfect-numbers: add iteration
ruby/phone-number: add iteration