This commit:
* renames `coresimd` to `core_arch` and `stdsimd` to `std_detect`
* `std_detect` does no longer depend on `core_arch` - it is a freestanding
`no_std` library that only depends on `core` - it is renamed to `std_detect`
* moves the top-level coresimd and stdsimd directories into the appropriate
crates/... directories - this simplifies creating crate.io releases of these crates
* moves the top-level `coresimd` and `stdsimd` sub-directories into their
corresponding crates in `crates/{core_arch, std_detect}`.
The official name of the memory intrinsics has changed to `memory.size` and
`memory.grow`, so let's reflect that with our naming as well! Additionally they
have an argument of which memory to operate on with LLVM and must always be zero
currently.
This exposes access to the `grow_memory` and `current_memory` instructions
provided by wasm in what will hopefully be a stable interface (the stable part
being x86 first in theory).
