Add rust runtime (#1597)

.gitignore

rust/.gitignore

rust/.rustfmt.toml

rust/.travis.yml

rust/Cargo.toml

rust/src/errors.rs

rust/src/lib.rs

rust/src/runtime/allocator.rs

rust/src/runtime/array.rs

rust/src/runtime/c_runtime_api.rs

rust/src/runtime/graph.rs

rust/src/runtime/mod.rs

rust/src/runtime/module.rs

rust/src/runtime/packed_func.rs

rust/src/runtime/sgx.rs

rust/src/runtime/threading.rs

rust/src/runtime/workspace.rs

rust/tests/.gitignore

rust/tests/build_model.py

rust/tests/test_graph_serde.rs