Move all spec testsuite into `/tests` directory.
So it means that several changes will happen:
- Compilation will share common dependencies in target directory. This should make CI builds faster. This also should reduce space requirements.
- Common Cargo.lock file
- `cargo test` will include spec tests.
- `cargo check --tests` will also include spec tests.
* 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
Nikolay Volf