This adds Rust support to Tundra

[emoon]

The following changes has been made:

• In DagGenerator.cpp if Annotation is set it's always being included when generating the hash. This allows the the Rust setup in an easy way make sure that dag nodes has a unique hash.
• In tools/rust.lua has been added which has the Cargo executable and rustc executable (not currently used)
• Added copy_file in file syntax/files.lua
• Rust-cargo has all the logic to handle everything to build correctly with Tundra. Cargo has some annoying things that it can't take target directory and external libs as command line parameters. This is being worked around by setting env variables on the same commandline as the the Cargo run command so it will be executed in the same process and thus won't collide which each other.
• Cargo will always write a target/(debug/release) directories if with a specified directory. The rust-cargo script writes the output like this t2-output/variant/__project_name/(debug/release) then a copy step of the executable/sharedlib is being done to the t2-ouput/variant directory. This keeps the structure where other Tundra artifacts are generated.
• In examples/rust some basic examples has been added that show how a C lib is being linked to a Rust binary and Rust shared lib. Also the Shared lib depends on an external crate that needs to fetch the dependices from creates.io and this is being tested also.

[deplinenoise]

Did you feel this was the wrong approach? I hadn't gotten around to reviewing the code yet.

[emoon]

No, I think the approach is correct and the PR work as expected and I use this in some projects already. I want to add another thing which is related to how on does (unit) testing with Rust and Cargo. The way it works pretty much is that if one can write something like this

#[test]
fn foo() {
   assert!(...);
}

This code is only executed when do cargo test on a project which is targeted at testing and there is a similar thing for benchmarks which has a #[bench] attribute to the function.

I would like to add support for that also but I really don't know how to do it but the changes as they are could be merged as is and this support could be added later.