Add a script to compile examples as an automated test suite.

* Added script/boostrap.sh to download the Arduino IDE and MPIDE (for
    chipKIT). Tested in Linux, should work in Cygwin and OS X too.
* Added script/runtests.sh to run "make" in each example project and
    collect the results. The script returns -1 if any fails.
* Moved currently testable examples to a "tests" directory, separate
    from examples that require alternative cores.
Add config for Travis CI to run the tests automatically.