Documented PHP Traversables

Classes in PHP extending from Traversable in PHP. Covering many PHP
extensions.
Diverse smaller changes

- Updated ForeachIterator
- Added some more tests and removed fluff from docblocks.
- Additionally fixed two little typos and added plates.
- Added missing @covers notations for tests FullCachingIterator;
  TraversableDecorator; CountableForeachIterator; IndexIteration.
Added composer support

Also expaneded file-comments / added plates and added COPYING file.