Set up Doxygen for Interface and domain server C++ code

tools/doxygen/README.md

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+# C++ Documentation Generation
+
+[Doxygen](https://www.doxygen.nl/) is used for generating documentation on parts of the C++ code.
+
+
+## Prerequisites
+
+**Doxygen** ≥ 3.9.1 - https://www.doxygen.nl/
+
+**Perl** ≥ 5.14 - http://strawberryperl.com/
+
+Make a `/build/doxygen/` directory.
+
+If you want to run Doxygen from a command prompt, add the Doxygen install's `/bin` directory to your system PATH.
+
+
+## Running
+
+### Using the Doxywizard GUI
+
+In the Doxywizard program:
+- File > Open `/tools/doxygen/Doxyfile`.
+- In the "Run" tab, click the "Run Doxygen" button.
+- Once it has compiled the documentation (this may take a while), click "Show HTML Output" to view the documentation generated.
+
+### From a command prompt
+
+Change to the `/tools/doxygen/` directory.
+
+```
+doxygen Doxyfile
+```
+
+Output files are generated in a `/build/docs/html/` directory. See the `index.html` file there.
+
+### Tips
+
+- The source code directory listed in the "Wizard" tab is only one of the directories scanned. For the full list, see the
+"Expert" tab's input category's settings.
+- The output directory is **not** wiped each time you run Doxygen, so you may want to periodically clear it out if you're
+finding it contains old, unwanted files.
+- If you want to iterate on a particular part of the documentation, you can temporarily change the "Source code directory"
+option in the "Wizard" tab of the Doxywizard program.
+
+
+## Altering the Doxygen configuration
+
+Most easily accomplished by using the Doxyfile GUI and using it to write a new `Libraries.Doxyfile` file.
+Alternatively, you can edit the `Libraries.Doxyfile` file in a text editor.
+
+
+## References
+
+- [Doxygen Web Site](https://www.doxygen.nl/)
+- [Doxygen Tutorial](https://embeddedinventor.com/doxygen-tutorial-getting-started-using-doxygen-on-windows/)
+- [Complete Guide On Using Doxygen](https://embeddedinventor.com/guide-to-configure-doxygen-to-document-c-source-code-for-beginners/)

tools/doxygen/jsdoc-filter.pl

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+# Filter out JSDoc comments by transforming them to ordinary comments.
+# (JSDoc comments are used to generate the user API docs and don't produce suitable results for the C++ docs.)
+while (<>) {
+    if (m/^\s*\/\*\*jsdoc/) {
+        print "\/*\n";
+    } else {
+        print;
+    }
+}