Commit 1a998886c8

Deprecates all existing std.io readers and writers in favor of the newly provided std.io.Reader and std.io.Writer which are non-generic and have the buffer above the vtable - in other words the buffer is in the interface, not the implementation. This means that although Reader and Writer are no longer generic, they are still transparent to optimization; all of the interface functions have a concrete hot path operating on the buffer, and only make vtable calls when the buffer is full.