Deprecate phar and pear installation, recommend composer
Merge pull request #231 from romainneutron/install-instructions

Deprecate phar and pear installation, recommend composer
Move tests to their own namespace, use composer autoloader for tests
Run composer install before running scripts
Remove composer.lock
Add --prefer-source option to composer command
Fix bug introduced in @cc9e1e8, Thumbnails may not have the right dimension