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Update .travis.yml

Try only updating the new ppa
Merge pull request #30 from bharrisau/travis-selective-apt

Run apt-get update for ppa only.
Freeze libstd on last known good commit.
Detached GPIO from GPIOConf (as it should have been in the first place).
Added basic gpio interrupt handling.
Bad ugly code for IRQ handling.
Added basic mrf driver and test application. Compiles but no tx/rx code yet.
Added sending code, demo now can talk to other devices.
Added basic irq handler.