Add changes-3.4.0

Change-Id: Idfd70d71a3290f4c3e9968f2882e7a671f8995d8
Reviewed-by: Christian Kandeler <christian.kandeler@theqtcompany.com>
Reviewed-by: Riitta-Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>

dist/changes-3.4.0

+Clang Static Analyzer 3.4.0
+
+* Removed experimental state
+* Added support for MSVC (requires Clang 3.6 or later)
+* Added support for MinGW
+* Added support for suppressing diagnostics
+  (added tool button in diagnostics view, and option pane in Projects mode)