This makes the version, arch, os tuple into a subdirectory to help
troubleshooting and cache management in general. The version is left
inside the binary key regardless.
Note: when installing via `go install ./cmd/wazero/...` the version ends
up as `dev`. This helps make that obvious. For example.
```bash
$ wazero version
dev
$ ./build/tinygo test -target wasi -c -o os.wasm os
$ wazero run -cachedir=$HOME/.wazero -mount=.:/ -env=HOME=. os.wasm -test.v
$ find $HOME/.wazero
/Users/adrian/.wazero
/Users/adrian/.wazero/wazero-dev-amd64-darwin
/Users/adrian/.wazero/wazero-dev-amd64-darwin/1f149f4bf475a33023ce33302780bee29ec08e89bd57cfbdf639c65c6009f1a4
```
Signed-off-by: Adrian Cole <adrian@tetrate.io>
67cc6d3779