At times we would like to provide types that do not implement
`PartialOrd` and `Ord` because it does not make sense. I.e., we do not
want users writing `a < b`. This could range from kind-of-iffy to
down-right-buggy (like comparing absolute locktimes).
However this decision effects downstream users who may not care about
what the ordering means they just need to use it for some other reason
e.g., to use as part of a key for a `BTreeMap` (as we do in `miniscript`
requiring the `AbsLockTime` type).
A solution to this problem is to provide a wrapper data type that adds
`PartialOrd` and `Ord` implementations. I wrote the `ordered` crate is
for this very purpose.
Feature gate a new dependency on `ordered` and implement `ArbitraryOrd`
for `absolute::LockTime`.
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