initial version of a quick-n-dirty mkdocs documentation. Works nicely so far

Limitations:
 - As site structure is made within a yaml file, you can't combine multiple project docs into one without writing an own index, which is redundant. HTML cross linking will be required, which doesn't seem too bad either
 - when referring to files to build, they are assumed to be underneath the doc directory. It's not possible to walk upwards, like ../../READEME.md, without messing up the file structure it builds. The problem can be worked around by making the site_dir deep enough, but it of course looks a bit odd. For now, symlinks are used, which restricts building the docs to posix systems

relates to #17
html pages live in gh-pages, therefore they won't clutter up and enlarge this tree

The good thing about it is that we can decide to drop the compiled configuration entirely.
This reminds me of the way mrv handles it's distribution files, which are put to a separate branch too - functionality I definitely want for bbuild
Merge branch 'issues/17' into issues/19

Done with the first experiment - believing it's a success