PhpDoc and some cleanup
Add missing phpDoc
Fix typo
Add php version requirement

The yield keyword is not available in <php55.
Merge branch 'hallabro-phpdoc'
Merge branch 'hallabro-composer-php55'
version bump to 2.0.0

previous refactoring changed public API
Throw NegativeRangeException when range is negative

Negative ranges would cause an infinite loop and eventually crash.
Clarify test
sprintf() not needed
Merge branch 'hallabro-negative-range-exception'
v2.0.1
php54 compatibility