Add read(io, ::Tuple) method to read multiple values at once

[sostock]

Inspired by this discourse thread, I think it would be useful to add a Tuple method to read (and write), so that one can do

a, b, c = read(file, Tuple{UInt8, Float32, Int16})

instead of

a = read(file, UInt8)
b = read(file, Float32)
c = read(file, Int16)

One can already work around this in a couple of ways, like

a, b, c = (read(file, T) for T = (UInt8, Float32, Int16))
a, b, c = read.(Ref(file), (UInt8, Float32, Int16))
a, b, c = map(T -> read(file, T), (UInt8, Float32, Int16))

but I think it would be nice to have an explicit method for it.

[JeffBezanson]

One issue here is alignment. A type like Tuple{UInt8, Float32} has alignment padding, so reading one is not the same as reading a UInt8 followed by a Float32. We could maybe use read(file, UInt8, Float32), but that prevents adding new trailing positional arguments to read in the future, and is also surprisingly hard to compile. For now a macro is probably the best solution actually, a, b, c = @read file UInt8 Float32 Int16.