Generate Protobuf from any other IDL

[Yawolf]

Related with #12

We need to add the ability to generate a Protobuf schema from these IDL:

• Avro
• Openapi
• Mu

[bilki]

I assign this myself to do a bit of sketching, to know if we have all the necessary pieces in place.

[bilki]

As of skeuomorph 0.0.11, we are missing all the necessary transformations:

• Avro to Protobuf (see Transform from Avro to Protobuf and viceversa skeuomorph#110, @AlvaroCaste is working on a bidirectional translation)
• Openapi to Protobuf
• Mu to Protobuf

[JesusMtnez]

Since schema transformations are out of the scope, I think this one should be closed.