Merge pull request #37 from jdreesen/simple-array-iterator

Use ArrayIterator instead of RecursiveArrayIterator for array input

Documentation updated to reflect latest changes

Merge pull request #26 from gzumba/remove-recursion-from-groupby

Build the arrays first directly and return them as Collections

Merge branch 'petemcfarlane-add-transpose-method'

New version tagged

Changelog updated

Only function now doesn't include item with key 0 in every result

ReplaceByKeys function added

Sum and average readme updated

Using float everywhere (instead of mixed double/float)