Issue #66 - Add documentation

Author: boretti

src/main/java/ch/powerunit/extensions/exceptions/ExceptionMapper.java

@@ -115,7 +115,7 @@ private boolean accept(Exception e) {
 	 * This method is used when ExceptionMapper are registered as default Mapper to
 	 * defines the right order to select then.
 	 * 
-	 * @return a ordering key, by default 0.
+	 * @return an ordering key, by default 0.
 	 * @since 2.2.0
 	 */
 	default int order() {

src/main/java/ch/powerunit/extensions/exceptions/package-info.java

@@ -56,6 +56,41 @@
  * Function<String, Optional<String>> functionWithOptionalResult =
  *   FunctionWithException.lifted(fonctionThrowingException);
  * </pre>
+ * 
+ * <h2>Exception Mapping</h2>
+ * 
+ * By default, the exception are transformed into a {@code RuntimeException}
+ * using the {@link ch.powerunit.extensions.exceptions.WrappedException}. This
+ * behaviour can be changed locally (second argument of the {@code unchecked}
+ * methods) or globally (by registering default {@code ExceptionMapper}.
+ * 
+ * To do the global configuration, it is required first to create the
+ * {@code ExceptionMapper}:
+ * 
+ * <pre>
+ * public class MyExceptionMapper implements ExceptionMapper {
+ *   public RuntimeException apply(Exception e) {
+ *     //TODO
+ *   }
+ *   public Class&gt;? extends Exception&lt; targetException() {
+ *     return //TODO;
+ *   }
+ *   // Optional, to define the order between the ExceptionMapper
+ *   public int order() {
+ *     return 100;
+ *   }
+ * }
+ * </pre>
+ * 
+ * Then, the {@code ExceptionMapper} must be registered :
+ * 
+ * <pre>
+ * module XXX {
+ *   requires powerunit.exceptions;
+ *   provides ch.powerunit.extensions.exceptions.ExceptionMapper
+ *     with ....MyExceptionMapper;
+ * }
+ * </pre>
  *
  * @see java.util.function
  *