Based on the original work by Justin Moon.
*MSRV unchanged from 1.29.0.*
When `std` is off, `no-std` must be on, and we use the [`alloc`](https://doc.rust-lang.org/alloc/) and core2 crates. The `alloc` crate requires the user define a global allocator.
* Import from `core` and `alloc` instead of `std`
* `alloc` only used if `no-std` is on
* Create `std` feature
* Create `no-std` feature which adds a core2 dependency to polyfill `std::io` features. This is an experimental feature and should be
used with caution.
* CI runs tests `no-std`
* MSRV for `no-std` is 1.51 or so
By exposing this, we can use the 'rand' dependency of secp256k1
in a project that only depends on rust-bitcoin without having to
add a separate dependency in order to activate the feature flag.
Devrandom
Andrew Poelstra
Sebastian Geisler
Steven Roose
Thomas Eizinger
Elichai Turkel
Carl Dong
Carl Dong