Eventually we would like all our crates other than `bitcoin` to be able
to be used without an allocator. Currently, and during crate smashing,
this is not that useful because so much of the code comes from `bitcoin`
and relies on the availability of an allocator.
As an initial step, add the `alloc` feature to `addresses` , `base58`,
and `primitives`.
In order to to keep `--no-default-features` builds working make the
crates empty if the `alloc` feature is not enabled. This is a suboptimal
solution because the error messages users will get when they forget to
enable `alloc` will be confusing (eg something like primitives does not
contain Transaction). However our CI script (`run_task.sh`) expects
`--no-default-features` to build cleanly (as do I).
Introduce an empty `bitcoin-primitives` crate.
We were give the name on crates.io and previously a version
`v0.1.16-alpha` was released so we use `v0.100.0`.
Tobin C. Harding