"std" feature

[termoshtt]

Copy of "next" branch in num
A clone of the original PR rust-num/num#296 with some fixes in ci/
Ref #16

[cuviper]

I appreciate your initiative, but I was hoping to do this in a way that preserves some authorship from before. I also don't want to include breaking changes like One::is_one yet, and I'm reconsidering my former reviews in rust-num/num#296 where I suggested #[cfg] on methods and said:

We should probably also add a caution in the docs for implementors of Float. Those that implement it normally are fine, but if someone now chooses to implement Float only for no_std, their build will fail if anyone else in the entire dependency graph enables num-traits/std.

In retrospect, this seems like something that will inevitably blow up. Maybe their original BaseFloat idea was enough, or some variation like the Real in #23. I'm tempted to just make Float depend on std with no baser alternative at all for now, and we can add something back in later.

[termoshtt]

but I was hoping to do this in a way that preserves some authorship from before

Your are quite right. I close this PR, and read the origitnal PR more carefully...