Zero-allocation encodings

[SSheldon]

Currently primitive types have encodings that do not allocate (they're defined from static strings) but compositions like structs either have to jump through hoops and use different encoding strings for different architectures or accept the cost of allocating a string and pushing the encoding of their fields.

Is there a better way to do this, where encodings from structs could more simply be composed without allocating?

[SSheldon]

My attempt at this is underway at SSheldon/rust-objc-encode

[SSheldon]

objc was updated to use objc-encode in 6092caa.