wolfSSL with Doxygen 1.8.13

---- Dependencies ----

cmake
make
git
latex-see below (With pdflatex included. However the pdflatex dependency can be removed by
setting USE_PDFLATEX to NO in the file "Doxyfile" located at
doc/formats/pdf/Doxyfile )

The following texlive packages were installed when creating this
documentation on Linux Mint:
sudo apt install texlive
sudo apt install texlive-latex-extra

For Mac users Basic Tex from TUG is recommended. After installing BasicTex
additional dependencies will need to be met:
% sudo tlmgr update --self
% sudo tlmgr install tabu varwidth multirow adjustbox collectbox sectsty tocloft collection-fontsextra

---- Generating the Documentation ----

If you are looking to just generate the html documentation and not interested in
how to add your own just run one of the following commands from the main wolfssl
directory:

    make dox (this option will make both html and pdf documentation)
    make dox-html (only html documentation)
    make dox-pdf  (only pdf documentation)

If it is the first time running one of the above commands the command will take
some time to run. This is because the doxygen repository must be clones and then
built along with the time taken to make the documentation.

Once documentation generation has completed to open the html use a browser to
open doc/html/index.html. To open the generated pdf looking for
refman.pdf located and doc/refman.pdf.

---- Configure ----

Doxygen uses a file called "Doxyfile" to hold all its values for configuration.
If needed, to generate a fresh Doxfile run the command

    doxygen -g

Once a Doxyfile is generate there are a few options to keep in mind.
Below are some the the settings that are currently used:

   EXTRACT_ALL

    - this option determines if all API are extracted or just API that is documented.

   OPTIMIZE_OUTPUT_FOR_C

    - changes the look and naming schemes used in generated documentation.

   RECURSIVE

    - allows doxygen to search subdirectories in a library for documenting.

   GENERATE_LATEX

    - tells doxygen whether or not to generate LATEX documentation. The Latex
      that is generated is used to generate a PDF as well.

   ENABLE_PREPROCESSING

    - tells doxygen whether or not to ignore C/C++ preprocessors directives i.e #ifdef, #ifndef

   EXCLUDE

    - allows the user to specify files or directories to ignore when documenting.

   HTML_EXTRA_STYLESHEET

    -allows the user to specify their own css style sheet to use for the doxygen html.

    SHOW_USED_FILES and SHOW_FILES

    - when using groups it is important to keep these options set to yes otherwise
    functions with documentation that are not part of a group may fail to be included
    in the generated documentation.

---- Embedding Documentation ----

Doxygen API documentation should be placed in the doc/dox_comments/
directory. The documentation should be stored in a file in this directory with the
same name of the file in which the API resides in the wolfssl repository. C code
header files (*.h) should be used when writing the API documentation. If API in a
file is being documented for the first time be sure to add the to the top of the
original file:

    /*!
        \file wolfssl/PATH_TO_FILE/FILE_NAME
    */

This ensures that the file will be linked to in the doxygen generated html.
When specifying a specific file with the \file command be sure to include part of
the file's path so that it is a unique name. This allows for linking to files even
when multiple files share the same name.

To ensure that doxygen documents a specific API in to a desired module be sure
to include that module's name in the \ingroup. The current modules to choose from
are as follows but new group can be made:

    \ingroup 3DES
    \ingroup AES
    \ingroup ARC4
    \ingroup BLAKE2
    \ingroup Camellia
    \ingroup ChaCha
    \ingroup ChaCha20Poly1305
    \ingroup Curve25519
    \ingroup DSA Algorithms
    \ingroup Diffie-Hellman
    \ingroup ECC
    \ingroup ED25519
    \ingroup HC128
    \ingroup HMAC
    \ingroup IDEA
    \ingroup MD2
    \ingroup MD4
    \ingroup MD5
    \ingroup PKCS7
    \ingroup Password
    \ingroup Poly1305
    \ingroup RIPEMD
    \ingroup RSA
    \ingroup Rabbit
    \ingroup SHA
    \ingroup SRP
    \ingroup wolfCrypt
    \ingroup openSSL
    \ingroup CertManager
    \ingroup TLS
    \ingroup CertsKeys
    \ingroup Setup
    \ingroup IO
    \ingroup Debug

If one of the above modules/ groups does not fit a desired function then a new
group will need to be created. To do this include add a new group definition
to the doxygen_groups.h file located at documentation/formats/pdf/doxygen_groups.h

    /*!
        \defgroup <group name> <description>
    */

The general outline when documenting within the wolfssl library in doxygen should
look like as follows:

    /*!
        \ingroup //if API should be in a separate module

        \brief <description of API>

        \return <name of return> <description> // each return will need \return.

        \param <name of param> <description> // stands for parameter, each parameter will need \param.

        _Example_
        \code
            // any example code here
        \endcode

        \sa // stands for see also. Each API reference here should begin with \sa
        \sa <Function>
        \sa <Function>
    */

When adding new documentation be sure to keep the sections, \ingroup, \brief,
\param, \return, Etc. separated with at least 1 newline. This insures that when
doxygen attempts to generate documentation the sections do not overlap each other
and produce errors (this is especially important when the latex is being generated).
Once finished creating new documentation it is highly recommended to generate new
html and pdf to ensure no errors were introduced that prevent documentation
generation and that the documentation shows up correctly.
