Doxygen documentation generator from sources for OpenFHE

[arcturusannamalai]

Add Doxygen for source browsing and implementation docs

To install Doxygen and Graphviz on Linux/Ubuntu you may run,

$ sudo apt-get install doxygen 
$ sudo apt-get install graphviz

To run and generate the docs you can run,

$ doxygen OpenFHE.Doxygen

which will populate the HTML in the 'html' folder.

To view the documentation,

$ cd html && python3 -m http.server 

you will be able to see the docs in the browser