Hash Consed Static Short String Storage

This crate is for storing static short strings (up to 256 bytes) in as compact a way as possible. Instead of each string getting it's own allocation, and associated padding, header, etc, they are stored packed into 1 MiB allocations. The length is stored in the allocation, making the stack size of the Str type 1 word instead of the usual 2 for &str. Because the length is limited to 256 bytes only one extra byte is used in the heap allocation for the length.