First pass at implementing support for a PSR-3 logger into xPDO.

The basic idea is you pass a LoggerInterface into the container, which will then be set to protected xPDO::$logger (provided by the LoggerAwareTrait).

The new xPDOLogger is a BC layer that provides a PSR-3 implementation for the old behavior. This also deprecates most of the old logger stuff, so that could be removed in v4.

Some to do's:

• Probably needs some new/updated tests
• Should xPDO::$logger be public? Kinda risks it getting replaced, but would simplify calls to it.
• Document usage
• Perhaps change xPDO::setLogger to also override the logger in the container?

For MODX-usage I'm thinking packages could provide a custom logger through the namespace bootstrap.php with setLogger(). Biggest challenge is that's after a bunch of other initialisation, including xPDO, so that might need some more thought.

For testing so far I used a quick snippet:

<?php
$modx->log(modX::LOG_LEVEL_ERROR, 'This is an error.');
$modx->log(\Psr\Log\LogLevel::ERROR, 'This is also an error.');
$modx->log(modX::LOG_LEVEL_INFO, 'This is not visible.');
$modx->setLogLevel(\Psr\Log\LogLevel::INFO);
$modx->log(modX::LOG_LEVEL_INFO, 'This is visible.');
$modx->setLogLevel(modX::LOG_LEVEL_INFO);
$modx->log(modX::LOG_LEVEL_INFO, 'This is also visible.');

$modx->setLogTarget('HTML');
$modx->log(modX::LOG_LEVEL_INFO, 'This gets rendered to screen.');


$modx->setLogTarget('FILE');
$modx->getLogger()->error('Hello world');
$modx->getLogger()->log('error', 'Goodbye world');