Update the version to 3.1.5

This was done by running misc/scripts/inc_release, bakefile_gen and
autoconf.

docs/doxygen/Doxyfile

@@ -6,7 +6,7 @@
 
 DOXYFILE_ENCODING      = UTF-8
 PROJECT_NAME           = wxWidgets
-PROJECT_NUMBER         = 3.1.4
+PROJECT_NUMBER         = 3.1.5
 PROJECT_BRIEF          =
 PROJECT_LOGO           = logo.png
 OUTPUT_DIRECTORY       = out

docs/readme.txt

@@ -1,4 +1,4 @@
-wxWidgets 3.1.4 Release Notes
+wxWidgets 3.1.5 Release Notes
 =============================
 
 Welcome to the latest development release of wxWidgets, a free and open source
@@ -16,7 +16,7 @@ more about wxWidgets at:
 
 Documentation is available online at:
 
-* https://docs.wxwidgets.org/3.1.4/
+* https://docs.wxwidgets.org/3.1.5/
 
 wxWidgets sources and binaries for the selected platforms are available for
 download from:
@@ -25,7 +25,7 @@ download from:
 
 or, for a more more permanent but less convenient to use link, from
 
-* https://github.com/wxWidgets/wxWidgets/releases/tag/v3.1.4/
+* https://github.com/wxWidgets/wxWidgets/releases/tag/v3.1.5/
 
 
 Changes since 3.1.3
@@ -36,7 +36,7 @@ commits from 74 unique contributors (37 with multiple contributions), so it is
 impossible to summarize all the changes in this document without making it too
 long, please see the fuller changelog at
 
-https://raw.githubusercontent.com/wxWidgets/wxWidgets/v3.1.4/docs/changes.txt
+https://raw.githubusercontent.com/wxWidgets/wxWidgets/v3.1.5/docs/changes.txt
 
 for more (but still not all) details, but some of the most important changes are: