Implement PSR-3

[danaki]

Please log using standard PSR-3, instead of error_log, thus a logger can be injected into objects.

[josecelano]

Thanks @danaki that's a good idea. I have to think how to add that change without breaking backward compatibility. I think we could add an ApiContext->setLogger(LoggerInterface ...)method to add an extra logger. That logger could be called in all places where we currently use BlockCypherLoggingManager. We can not totally replace that one becuase I think it's very useful to have a out-of-the-box logger without defining you own logger. We should also implement LoggerInterface in BlockCypherLoggingManager.

Anyway I do not have too much free time to do it rigth now.