Writing lower case numpy dtype field names is a "nono"

[goodboy]

Got bit by this and documented it in alpacahq/marketstore#324. I feel that writing a test would be handy for tracking as well as maybe some protection client-side to avoid users hitting this.

2 questions:

• should the client maybe do better error reporting from the server? Right now this is being deferred to user client code. I wonder if a flag like Client(raise_response_errors=True) would be handy?
• There should be something in the docs stating that you can't use lower case structarray field names or even make Client.write() check for capital field names? This situation makes me think that the Client.create() approach (from Improvements #37) would allow for this without having to check in every .write() call.