use hyde as a clang-doc generator

Hi!

A friend of mine recommended this tool and I would like to use it on my libraries. I really like the output format, easy to read and easy to document. My only issue is integrating the tool itself into my build systems and pipelines.
My main idea was to use the compile_commands.json provided by cmake, but it seems this tool is not ready to accept multiple translation units.

**Is your feature request related to a problem? Please describe.**
This tool aims to provide documentation based on clang ast. There is already a similar tool in the llvm environment itself, called [clang-doc](https://github.com/llvm/llvm-project/tree/main/clang-tools-extra/clang-doc). Would it be possible to merge the efforts of this project into that one?

**Describe the solution you'd like**
In my opinion the easiest solution would be to merge this repository into the clang-doc as a generator format. This would require minimal modification in the clang-doc itself, but would require acceptance.

**Describe alternatives you've considered**
Another option would be to extend clang-doc to accept external formatters, such as hyde. This would require modification in the clang-doc as right now it is not ready for that. Would also require modification in the hyde code base, but it would be very similar to the other approach. ( Fit to the [Generator](https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/clang-doc/Generators.h) interface. )

**Additional context**
One option would be to support multiple translation units via [Executor](https://clang.llvm.org/doxygen/classclang_1_1tooling_1_1ToolExecutor.html), but it would cause duplicate effort because clang-doc already does this.