[Ada] Update gnatpp documentation after engine change

2018-01-11  Bob Duff  <duff@adacore.com>

gcc/ada/

	* doc/gnat_ugn/gnat_utility_programs.rst: Rewrite gnatpp documentation
	to match what the Libadalang-based version does.
	* doc/gnat_ugn/about_this_guide.rst: Update reference.

From-SVN: r256500

gcc/ada/ChangeLog

+2018-01-11  Bob Duff  <duff@adacore.com>
+
+	* doc/gnat_ugn/gnat_utility_programs.rst: Rewrite gnatpp documentation
+	to match what the Libadalang-based version does.
+	* doc/gnat_ugn/about_this_guide.rst: Update reference.
+
 2018-01-11  Hristian Kirtchev  <kirtchev@adacore.com>
 
 	* sem_res.adb (Uses_SS): A controlled type requires the secondary stack

gcc/ada/doc/gnat_ugn/about_this_guide.rst

@@ -146,7 +146,7 @@ the new document structure.
     - :ref:`The_Ada-to-XML_Converter_gnat2xml`
     - :ref:`The_Coding_Standard_Verifier_gnatcheck`
     - :ref:`The_GNAT_Metrics_Tool_gnatmetric`
-    - :ref:`The_GNAT_Pretty-Printer_gnatpp`
+    - :ref:`The_GNAT_Pretty_Printer_gnatpp`
     - :ref:`The_Body_Stub_Generator_gnatstub`
     - :ref:`The_Unit_Test_Generator_gnattest`