Changes before initial release to master branch

[matthijskooijman]

Some things that we should do that might involve history rewriting and must be done before creating a master branch. Feel free to add things.

• Add general README
• Add Arduino README
• Make Arduino export script work on OSX (use ln instead of cp --symbolic-link)
• Test on stm32
• Convert odt/pdf documentation to markdown/rst/something else? Perhaps remove files for now and convert them later?
• Rename config macros to CFG_something (or otherwise make them consistent)
• Convert to standard integer types (uint16_t instead of u2_t) for portability and preventing conflicts.
• Change ostime_t to unsigned, introduce ostimediff_t for subtractions?
• Fix big vs little endian voor ids etc?