Improvements for Logger

[ADDED] Methods to check if the log message is FALTAL, ERROR or WARN
[ADDED] Check log level before writting the log message
[ADDED] Some more log methods with variable parameters. Now Vert.x can log messages with parameters. Example:

logger.info("Example message with {0} and {1}", "parameter 1", "parameter 2");

Prints: "Example message with parameter 1 and parameter 2"