Add benchmarks to compare different structures

[c410-f3r]

Useful to see how rust-decimal is performing compared to other libraries or how much is lagging behind f32 or f64 hardware based operations.

As seen from above, rust-decimal is the fastest decimal library with operations ~2000% slower if compared to native primitives.

[paupino]

This is cool to see. Also cool to see that criterion and cargo-bench can exist together just fine.

[c410-f3r]

Hum... I was thinking about removing comparisons between other rust libraries to prevent ppl pointing fingers and reduce the amount of development dependencies. So the only thing that would remain is the comparison between rust-decimal and native floating primitives

[paupino]

Oh yeah - fair call. Perhaps a separate repo could compare all libraries instead - it is quite useful to keep track of over time but perhaps not the responsibility of this library/repo.

[c410-f3r]

Oh yeah - fair call. Perhaps a separate repo could compare all libraries instead - it is quite useful to keep track of over time but perhaps not the responsibility of this library/repo.

Indeed! Another repository would be the best approach so feel free to create one if desired

[paupino]

I reverted this PR but more than happy to include again for just f32/f64! One additional thought actually - I wonder if we need to do different numbers for a and b. I'm curious whether other libraries try to optimize on this scenario - much like Rust Decimal does (e.g. same scale, 32 bit divisor)!