Support Rust

[eldipa]

Describe the feature you'd like
byexample supports C/C++ so Rust is the reasonable next step. A quick PoC with evcxr, the interpreter for rust, shows that it is viable but not without some hard corners.

Additional context (optional)
We need a way to disable the color from the output. Perhaps a simplified processing with pyte ? #180

[eldipa]

The first PoC gave really good results. evcxr works quite well with byexample but there are still some unresolved issues:

• stdout/stderr output from the example is printed by evcxr in background so in some cases the output arrives after the prompt. A quick hack is to add a delay after the prompt and a subsequent output read trying to get the missing few bits (-x-delayafterprompt flag). But it is fragile, see Use last line of the expected output to sync with the interpreter in addition to the prompt #181
• evcxr is very slow. In theory the compiled examples could be cached using sccache but I couldn't make it work:sccache keeps saying that the compiled snippets are Non-cacheable calls.

[eldipa]

About sccache, evcxr/evcxr#184