Cleanup documentation and extra files (#27)

* Cleanup documentation

* remove duplicated folder

* Remove unused VERSION file

* Remove more duplicated files

* Remove more unneeded files

Author: chingor13

ext/Dockerfile

@@ -132,7 +132,7 @@ public function tracer()
      *
      * @param array $spanOptions Options for the span.
      *        {@see OpenCensus\Trace\TraceSpan::__construct()}
-     * @param callable $callable    The callable to inSpan.
+     * @param callable $callable The callable to instrument.
      * @return mixed Returns whatever the callable returns
      */
     public function inSpan(array $spanOptions, callable $callable, array $arguments = [])