Packed fields

[jwroblewski]

Added support for packed fields.

[codekitchen]

Hey sweet, thanks. The Travis build is failing because it doesn't have the compiler available when running the tests -- see how I fixed the other tests in a479dbb

Alternatively, I've been digging through the Travis documentation and it looks like I should actually be able to install protobuf/protoc before the build starts from an apt package, I just need to figure out the right magic to make it happen.

[jwroblewski]

Would be nice to have protoc available on travis. Check out the below .travis.yml, it downloads and installs protoc directly from sources:

https://github.com/christiankerl/org.eclipselab.emf.ecore.protobuf/blob/master/.travis.yml

[jwroblewski]

I fixed the specs, so travis is now green even w/o protoc installed. I also squashed all the commits, so the complete feature is now in a single place (eac5a7e).

[codekitchen]

Looks great, thanks for the contribution. Good link to that travis file too, I'll try to get protoc installed on travis runs soon.