* .travis.yml :
      - Added PHP 5.4 tests

  * composer.json :
      - Updated PHPUnit requirement to be >= 3.7

  * General :
      - Added PHPDoc headers to source files

  * BackoffCaller.php :
      - added a delay callback that is called to handle the actual delay instead of just calling sleep().

  * BackoffExponential.php :
      - fixed bug that prevented decimal exponents
      - fixed implementation that caused the backoff to be non-exponential

  * BackoffMultiplicative.php :
      - Initial commit

  * Backoff.php :
      - Implemented a proper autoloader
      - Removed unused code/quick autoload hacks

  * readme.md :
      - Added BackoffMultiplicative
      - Minor formatting changes
      - Updated to reflect code changes
merge fix