Draft: melior book and toy example

[gavrilikhin-d]

This is a work in progress PR for implementing Toy language example in melior.

I need some guidance from you @raviqqe, because I: a. never used MLIR b. never wrote a documentation book c. isn't a native english speaker

Any edits and help would be appreciated.

[raviqqe]

Hmmm, I'm not sure if Melior is mature enough to write a book about it. As described in the readme, both MLIR and its C API are still unstable in terms of their API.

Also, Melior has almost 1-to-1 relationship with the MLIR C API. So, I think what we should do is rather contribute to the LLVM project itself or create another project of MLIR tutorial book. Then, interpreting the tutorial codes in C++ into Rust should be straightforward. WDYT?