More efficient protobuf format

Don't serialize everything as string but check the data type.
Next iteration of protobuf format (WIP)

Some more changes in the protobuf format, and the matching implementation

This code has not yet been tested, and tests have not been updated. This commit is just so others can continue this tomorrow.
Further improvements. Integration tests working
Functional tests fixed after protobuf refactoring/optimization
Small simplification

Remove a superfluous data copy
Adjust to changed core API and enable CompileStatic

Use the exposed types from core API to select to generate Double columns or string columns.
Enable CompileStatic and trim a lot of now superfluous code, as the new serialization is quite a bit simpler.
Add a few comments and shorten imports
Merge pull request #21 from thehyve/refactor/optimize_protobuf

Refactor/optimize protobuf