conv is unmaintained

[jayvdb]

c.f. #2199

conv is one of the main two remaining usages of custom_derive, and is by the same maintainer, who has not been contactable.

DanielKeep/rust-conv#14 and DanielKeep/rust-conv#16 are examples of serious issues that have been ignored.

I'll start looking for alternatives.

[jayvdb]

Some alternatives:

• https://crates.io/crates/num-conv (used by time crate, so likely already in dependency tree)
• https://github.com/Clikengo/usize_cast and https://crates.io/crates/convi for usize <-> u64/u32 conversions
• az
• num-traits