Adding support for cm900 and opencm904 boards (robotis)

This adds support for the following boards:

* `cm900`: [Robotis CM900](http://support.robotis.com/en/product/auxdevice/controller/cm-900_manual.htm)
* `opencm904` [Robotis OpenCM9.04](http://support.robotis.com/en/product/auxdevice/controller/opencm9.04.htm)

Everything was not tested

I must warn that the boards-specific code come from the ROBOTIS IDE (https://github.com/robotis-pandora/ROBOTIS-OpenCM), which uses a mod of the libmaple, and was changed to fit with the full original libmaple, so we may have to check for licence issues