Restructure code layout, add make tasks

- Add all_firmwares make target which builds all firmwares
  utils/buildall.sh used to do this
- Add astyle task which runs astyle on src/*.h
- Add rules to the astyle config file
- Make all_firmwares the default make target
- Move the astyle config to etc/
- Use astyle reformat with the new rules
- Put all temporary build files into out/tmp
- Rename the output firmware file to out/{tx,rx}-{board_type}.hex