Minor fixes to handle a .proto option and show a missing CLI option

I used your code generator to process a realtime GTFS transit feed protocol file (see https://developers.google.com/transit/gtfs-realtime/gtfs-realtime-proto) - it's saved me at least a couple of days work! :)

However it did trip over one of the options in the .proto file (a `syntax` option), which your processor didn't handle. It's not something that the processor requires, but it did get in the way, so I've added a small fix for it (see `CodeGenerator/ProtoParser.cs` lines 95-99).