add a zero-copy, safe, symtable for use in no std

[m4b]

It would pass out references to Syms, which are byte-casted from a backing &[u8]; and have a new -> Result api (which validates the bounds). We'd need two for elf32 and elf64 probably; or we can initialize as 32 or 64 bit (or pass a container context, which has less boolean blindness). This will be tricky and annoying I think due to type name punning stuff, so probably easiest to just add two typed versions and re-export it

Similar to strtab, I would also want it to implement Index, so it can be literally drop-in replaced in code that previously used a &[Sym].

Another approach could just provide a newtype wrapper on &[Sym] that validates the backing bytes and a count provided, and then Derefs to a &[Sym] so we get indexing for free.

Lots of options.

If we want to get fancy-pantsy, we might be able generify it to both ELF and Mach symbols, and have it return references via something like:

get::<Symbol>(index) -> Result<&Symbol>

but that might not be worth the effort.

[m4b]

I think parts of this are implemented; not as interesting, so closing