API CHANGE: Debug::showError(), Debug::showLines(), Debug::log(), and Debug::header() removed
NEW: Logging provided
ZendLog has been removed and monolog introduced instead as a dependency.
The “ErrorLogger” injection point is now the used as the logger that
errors are fed into, and implements PSR-3’s Psr\Log\LoggerInterface.
The SS_ERROR_LOG setting expect a Monolog Logger to be provided as the
ErrorLogger.
