Add a conventional Rust layer to ittapi_rs

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Working with ittapi is not the most simple thing I have done (😁) and, in order to increase adoption and speed up integration with other projects, I could use a shim layer that makes ittapi_rs use Rust conventions (e.g., it could pass around &str instead of *const c_char). What is published currently corresponds to a *-sys crate: a direct transcription of the C API to Rust. I am requesting a higher level crate built on top of that.

The intel-seapi crate had this higher-level API--see the docs. But that crate is no longer maintained. Can we add this type of functionality to ittapi_rs, potentially creating separate ittapi and ittapi-sys crates?

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This is now in-tree; see #45 and #48.