This commit prepares a release

I personally would have waited for Kuba's changes to be complete. But
the current wxMaxima is so much faster, much more stable and
user friendlier than the last release that we can dare to release
the current state to the public, anyway.

Author: gunterkoenigsmann

CMakeLists.txt

@@ -14,7 +14,7 @@ else()
 endif()
 
 project(wxmaxima LANGUAGES CXX)
-set(VERSION 20.04.0-DevelopmentSnapshot)
+set(VERSION 20.06.0)
 set(GITVERSION ${VERSION})
 set(PACKAGE wxmaxima)
 set(APP_NAME wxmaxima)

NEWS.md

@@ -1,15 +1,17 @@
-#Current
+#20.06.0
  * Many spell corrections and bugfixes
  * Updated Russian translation by OlesyaGerasimenko
  * Updated Ukrainian translation by Yuri Chornoivan
  * Many corrections to the german translation
  * The history sidebar now works again
  * TextCells with copy-alt-text caused an crash
  * A few additional small bugfixes
+ * Many (really many!) big stability improvements
  * in sqrt(conjugate(f(x))) the horizontal lines coincided
  * Strings were searched for comment starts when adding line endings
  * Faster start-up by avoiding unneeded redraw events
  * A big number of performance improvements
+ * Unfortunately one last temporary fix reduces performance again
  * Corrected a bug that sometimes caused parts of equations not to be displayed
  * As this allows to improve performance and stability C++14 is now used
  * Speed boost The list of anchors from the manual is now cached on disk

data/io.github.wxmaxima_developers.wxMaxima.appdata.xml

@@ -51,6 +51,33 @@
     <content_attribute id="social-info">mild</content_attribute>
   </content_rating>
   <releases>
+    <release version="20.06.0" date="2020-06-04">
+      <description>
+	<p>
+	  A release that allows to include the current state of improvements
+	  to the maxima windows installer.
+	</p>
+        <ul>
+	  <li> Many spell corrections and bugfixes </li>
+	  <li> Updated Russian translation by OlesyaGerasimenko </li>
+	  <li> Updated Ukrainian translation by Yuri Chornoivan </li>
+	  <li> Many corrections to the german translation </li>
+	  <li> The history sidebar now works again </li>
+	  <li> TextCells with copy-alt-text caused an crash </li>
+	  <li> A few additional small bugfixes </li>
+	  <li> Many (really many!) big stability improvements </li>
+	  <li> in sqrt(conjugate(f(x))) the horizontal lines coincided </li>
+	  <li> Strings were searched for comment starts when adding line endings </li>
+	  <li> Faster start-up by avoiding unneeded redraw events </li>
+	  <li> A big number of performance improvements </li>
+	  <li> Unfortunately one last temporary fix reduces performance again </li>
+	  <li> Corrected a bug that sometimes caused parts of equations not to be displayed </li>
+	  <li> As this allows to improve performance and stability C++14 is now used </li>
+	  <li> Speed boost The list of anchors from the manual is now cached on disk </li>
+        </ul>
+      </description>
+    </release>
+
     <release version="20.04.0" date="2020-04-18">
       <description>
 	<p>