Implement TinyG simulator and run first simulator tests on Travis

Hi Alden,

this CL adds the first version of TinyG simulator. Its current state, future plans and other details are covered by the [sim/readme.md](https://github.com/krasin/TinyG/blob/minisim/firmware/tinyg/sim/readme.md).

Please, review this series of commits and let me know if something needs to be changed. Note: this changelist is quite large, so I do expect some comments and am willing to address them.

krasin