Merge branch 'update_submodules' of https://github.com/MaartenBent/wxWidgets

Update all 3rd party libraries to the latest versions.

See https://github.com/wxWidgets/wxWidgets/pull/1023

docs/changes.txt

@@ -115,6 +115,7 @@ All:
 - Avoid spurious errors on thread creation under NetBSD.
 - Improve high DPI support in wxAui (Simon Rozman).
 - Fix a bug with parsing time zones in wxDateTime::ParseFormat() (evileye).
+- Update all 3rd party libraries to their latest versions (Maarten Bent).
 
 All (GUI):
 

docs/contributing/how-to-update-third-party-library.md

@@ -42,7 +42,14 @@ one:
     $ git push --set-upstream git@github.com:wxWidgets/libexpat.git wx
 
 
-3. Updating the main repository
+3. Generating build files (libexpat, libtiff)
+---------------------------------------------
+
+We include the generated build files of libexpat and libtiff. For libexpat run
+`buildconf.sh`. For libtiff run `autogen.sh`. Commit the changes.
+
+
+4. Updating the main repository
 -------------------------------
 
 If there are any changes to the source files used by the library, update the
@@ -54,7 +61,7 @@ manually.
 Commit these changes and the submodule and create a PR to test them as usual.
 
 
-4. Special instructions for libpng
+5. Special instructions for libpng
 ----------------------------------
 
 We use a special hack for libpng as we want to prefix all its symbols with