Refactored Project

Stream.php now implements iteratoraggregate so that points can be iterated over
Can now update single points in a stream using setPointAt() as well. Point.php
was removed due to lack of utility. Created common interface for all Stream
operations. Created an abstract base class for all operations as well.
Renamed ValidStreams.php to StreamValidator.php. Along with other general
refactoring and test re-writing.