New C++ Api: Initial setup of Api documentation. (#6295)

This configures the initial setup for generating Api documentation with
Sphinx via Breathe and Doxygen. All fixes in the documentation of the
cvc5.h header are for the purpose of eliminating warnings. This PR does
not check for completeness of the documentation, and does not yet tweak
the documentation to be nice, beautiful and consistent, which is
postponed to future PRs.

Configure with `--docs`, and then make. This will generate a `docs`
directory in the build directory. The Sphinx documentation can be found
at `build/docs/sphinx/index.html`. Doxygen documentation is only
generated as xml under `build/docs/doxygen`.

This PR further proposes a new style for copyright headers. If this
style is approved, I will submit a PR to update the update_copyright.pl
script.

1 files changed, 17 insertions, 0 deletions

diff --git a/INSTALL.md b/INSTALL.md
index 2d124b2af..1e4ce607e 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -201,6 +201,23 @@ bindings for `<lang>`.
 If you're interested in helping to develop, maintain, and test a language
 binding, please contact one of the project leaders.
 
+
+## Building the API Documentation
+
+Building the API documentation of CVC4 requires the following dependencies:
+* [Doxygen](https://www.doxygen.nl)
+* [Sphinx](https://www.sphinx-doc.org)
+* [Breathe](https://breathe.readthedocs.io)
+
+To build the documentation, configure CVC4 with `./configure.sh --docs`.
+Building CVC4 will then include building the API documentation.
+
+The API documentation can then be found at `<build_dir>/docs/sphinx/index.html`.
+
+To only build the documentation, change to the build directory and call
+`make docs`.
+
+
 ## Building the Examples
 
 See `examples/README.md` for instructions on how to build and run the examples.