documentation: update API documentation

Update documentation for better readability.
documentation: enable generation of documentation

Link the shell script in doc/ with the make file to provide an easy to use
interface.
documentation: clear up README.md

Remove all development specific information out of README.md and place
it into the new guidance in doc/.

Only leave the compilation-specific hints in README.md.
documentation: provide full documentation

By using the Linux kernel helper to generate an XML file out of the
structured code comments, man pages, HTML files, a PDF file, or a PS
file can now be generated.
version bump: 0.2.1

Bump version to indicate documentation update.
version bump 0.2.1: list changes