Add params method to Network

[Kixunil]

Writing network.params() is less annoying than Params::network(), so this adds it. Making it return a static could also improve performance.

Didn't do Params -> Network conversions because of #2173

[apoelstra]

Would suggest drafting this and discussing in #2169 or #2173 (pick one :)) to decide how we want these two types to relate.

[Kixunil]

I don't think they are exclusive unless type Network = &'static Params; which I don't like much.

[apoelstra]

What about struct Network<'a>(pub &'a Params)?

We definitely shouldn't make Network be an alias of &'static Params because that makes non-static Params second-class and kinda defeats the purpose of even having the structure.

[Kixunil]

Putting a lifetime everywhere you had Network would be super annoying. I wouldn't be surprised if people rage quit. I'd consider doing so myself.

[apoelstra]

Hmm, yeah, that's a very good point.

[Kixunil]

Force push only fixes a typo in the commit message.

[apoelstra]

9282cc4 looks good to me. I wonder if we should use AsRef rather than From<X> for &'static Y though.

[Kixunil]

It felt kinda weird to return a reference from AsRef that isn't stored in the value itself. I guess I will ask at Rust forum what people think.

[Kixunil]

https://users.rust-lang.org/t/implementing-asref-for-types-not-storing-the-reference/102147

Now that I wrote it I'm very tempted by the boxes&co argument but still interested in other viewpoints. :)

[tcharding]

ACK 9282cc4

[tcharding]

FWIW, in my opinion just simple network.params() seems better than using AsRef or From.

[apoelstra]

ACK 9282cc4