Fix kconfig_compiler doxygen formatting
This improves the doxygen formatting of src/kconfig_compiler/README.dox.
- Doxygen sections instead of markdown list items (!) and HTML headers
- More descriptive section titles
- HTML Definition list instead of a wide HTML table for compiler options
- HTML Definition list instead of a markdown item list for data types
- Syntax highlighting for examples
The content is not modified, only the formatting.
Screenshot: (before/after)