Remove all old test fixtures that migrated in this repo from the parity-wasm.
Also, use .wast files instead of compiled .wasm. I believe this is more convenient than testing a .wasm file and having a corresponding .wast file, which might go out of sync.
* Initial implementation
* Not use grow as it is makes debug builds very slow
* Use Pages::BYTE_SIZE for LINEAR_MEMORY_PAGE_SIZE
* Tidy docs.
* Use memory_units from git.
Sergey Pepyakin