Add doxygen-1.8.20. (#4779)

* Add doxygen-1.8.20.

* Fix switches.

manifests/DimitriVanHeesch/Doxygen/1.8.20.yaml

@@ -0,0 +1,18 @@
+Id: DimitriVanHeesch.Doxygen
+Version: 1.8.20
+Name: Doxygen
+Publisher: Dimitri van Heesch
+License: Copyright © 1997-2018 by Dimitri van Heesch.
+LicenseUrl: http://doxygen.nl/index.html
+AppMoniker: doxygen
+Tags: documentation, generator
+Description: Doxygen is the de facto standard tool for generating documentation from annotated C++ sources, but it also supports other popular programming languages such as C, Objective-C, C#, PHP, Java, Python, IDL (Corba, Microsoft, and UNO/OpenOffice flavors), Fortran, VHDL and to some extent D.
+Homepage: http://www.doxygen.nl/index.html
+InstallerType: inno
+Installers:
+  - Arch: x86
+    Url: http://doxygen.nl/files/doxygen-1.8.20-setup.exe
+    Sha256: 30f19774d7cbceddfb678bb411b969b4f3d370ecc5c56f268e40e6b3049c07a7
+    Switches:
+      Silent: /verysilent /norestart
+      SilentWithProgress: /silent /norestart