Fixed slf4j dependency
Fixed slf4j dependency

* Changed dependenc from slf4j-binding to the slf4j-api. The library can be used without any additional dependencies and, in that case, will produce no logging output whatsoever.
* In order to produce logging output with your preferred concrete logging frameword, add a depency to the respective binding. For instance slf4j-jdk14 for JUL, slf4j-log4j12 for Log4J, or logback-classic for the native implementation of the API
* See also http://www.slf4j.org/manual.html#swapping

oxo42/stateless4j