std.fmt: use SI prefixes for printing bytes
std.fmt: use SI prefixes for printing bytes

closes #1015

Dimenus/zig,zig-lang/zig,raulgrell/zig,andrewrk/zig,andrewrk/zig,zig-lang/zig,zig-lang/zig,Dimenus/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,Dimenus/zig