Zig breaking change – Initial Writergate

I find the `Reader.stream(writer, limit)` and `Reader.streamRemaining(writer)` functions to be especially elegant to build a push-based data transformation pipeline (like GREP or compression/encryption). You just implement a Writer interface for your state machine and dump the output into another Writer and you don't have to care about how the bytes come and how they leave (be it a socket or shared memory or file) -- you just set the buffer sizes (which you can even set to zero as I gather!)

`Writer.sendFile()` is also nice, I don't know of any other stream abstraction that provides this primitive in the "generic interface", you usually have to downcast the stream to a "FileStream" and work on the file descriptor directly.