Improve RESTEasy documentation

Chapter "2.2.1. JAX-RS 2.0 Client API":

"You have to add dependency for users of the Maven project:"
->
"You have to add dependency for RESTEasy client to your Maven pom.xml file:"

–

"can modify the Response object before it is handed to the application code. For example:"
->
"can modify the Response object before it is handed to the application code. Here's some pseudo code to illustrate things:"

See this upstream documentation

Chapter "2.3.1. Mapping Extensions to Media Types"

Add this text to the end of this chapter to the example part:

Possible url variants for "http://localhost:8080/my-application/test" basic url:
* http://localhost:8080/my-application/test.html
* http://localhost:8080/my-application/test.json
* http://localhost:8080/my-application/test.xml

Chapter "2.3.2. Mapping Extensions to Languages":
Add this text to the end of this chapter to the example part:

Possible url variants for "http://localhost:8080/my-application/test" basic url:
* http://localhost:8080/my-application/test.en
* http://localhost:8080/my-application/test.es
* http://localhost:8080/my-application/test.fr