Add Rust Driver

[wyhaya]

• Add crossdb as a submodule to this repository, using static link.
• Windows is currently not supported.
• There are some warnings when linking crossdb, which may be fixed later.
• Currently, there is only one exec API, which is very limited; overall, this is a good start.
• @kolinfluence Please feel free to overwrite when you are done.

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@jcwangxp Maybe need to create a crate on crates.io so that we don't have to use git to access it.

[jcwangxp]

Thanks for the your work, could you help to create a crate on crates.io, I'm not rust guy :)