Removed direct psr/log inclusion (moved to composer-dependency)

General cleanup:
- deleted lib/Psr
- introduced composer-dependency on psr/log 1.*
- added test/boostrap.php to use composer-autoloader for text-execution,and changed phpunit.xml.dist accordingly
- changed .travis.yml to use both php5.3 and php5.4 for test-execution
- changed .travis.yml to properly load composer dependencies and execute tests with code-coverage
- introduced a .gitignore file for /vendor and composer.lock