Updated some resources references after first release.
Added symlink to contributors guide to be caught by GitHub.
Build testing against PHP 5.5.
Refactored tests to use PHPUnit mocks.
Minimized Composer output in Travis.
Text output of code coverage after tests to make it visible in Travis.
[#1] Filesize helper.
Path resolving method utility.
[#3] File storage abstraction.
[#23] Used vfsStream for tests.