Tech requirement for units

Hello,
there seems to be an [issue with units](https://github.com/Blizzard/s2client-proto/blob/33f0ecf615aa06ca845ffe4739ef3133f37265a9/s2clientprotocol/data.proto#L91) that have 2 requirements, e.g. Thor has techlab and armory requirement, Ghost has techlab and ghost academy requirement, Battlecruiser has techlab and fusion core requirement.

However, in the API they all return UnitTypeData.tech_requirement = 0
Also Siegetank seems to return id=5 which is just `TECHLAB`. Wouldn't it be better to return at least `FACTORYTECHLAB` or `FACTORY and TECHLAB`? There are a few more cases like these actually.
Or is that intended behavior that the `tech_requirement` requirement basically only works for buildings?

I'm using [Dentosal's API](https://github.com/Dentosal/python-sc2) but it should still be an issue with the s2client-proto, that is why I'm creating the issue here.

Start with the linked data.proto definition around line 91 and inspect how UnitTypeData.tech_requirement is represented for Thor, Ghost, Battlecruiser, and Siege Tank. Compare those protocol values with the behavior observed through Dentosal's python-sc2 API; done means the intended handling of multiple unit technology requirements is documented or consistently represented.

Written by the indexing model from the issue text.