[Feature request] Add support for reading FixedPointNumbers

It would be great if FixedPointNumbers could add support for the `read` function, i.e. `read(io, N4f12)`, that would handle the padding and other issues. For example, given a 24-bit long stream, the output of the function would be a vector of two `N4f12`s.

This recently came up in https://github.com/tlnagy/TiffImages.jl/issues/58, but I feel like this package is a better home for such logic. I could make an attempt at an implementation if people feel like this is the best location for it.