New formula: nanopb-generator

Nanopb is an ANSI-C library for encoding and decoding messages in Google's Protocol Buffers format with minimal requirements for RAM and code space. It is primarily suitable for 32-bit microcontrollers.

This formula contains the code generator part of nanopb.
Vendor protobuf python library
A real test
nanopb-generator: add 0.2.7 bottle.