This patch implements the enacl:crypto_sign_ed25519_sk_to_pk/1 for
generating the public key from a given Ed25519 secret key.

Force remove artifacts in clean target.

Investigation shows erratic behaviour of the CSPRNG. It may block at times
because it needs to go to the kernel and obtain more random information in
the system. Once this happens, you are blocked for quite a long time, but
we don't generally know when this happens. So just execute these directly
on the dirty scheduler.

Make sure these either execute on the Dirty Scheduler or execute with bumping
reductions.

Some operations are simply too expensive. Always run these on the dirty
scheduler.

the project.

Rather than creating a set of <<0,…,0>> every time and then throwing it away,
we now reuse a constant. They are small enough they are still small-binaries, but a
process can keep them around and use them whenever it needs to go to the
low-level area.

We have a better way to handle this. So we are going to handle it in a better way, by
simply making the direct solution: Fix the crap by using DTrace.

* Introduce enacl:verify/0 to verify the integrity of the library.
* Always run keypair functions on the dirty schedulers.
* Do not call NIFs when creating zerobytes. Avoid constructing new binary data, but reuse a constant.
* The box/box_open and box_seal/box_seal_open API is so expensive to call there is little overhead in
  running it on the DS always.

* Call the functions `box_seal` and `box_seal_open` to match the libsodium names in module `enacl`.
* Fix a bug in the C NIF: We should fail if the input is `<` SEALBYTES but not on `<=` SEALBYTES. The latter made it impossible to encode empty messages.
* Add variants which run directly on the interpreter scheduler for small messages.

Also:

* Provide full EQC functions for the testing purposes. This generated around 13000 random test cases in a 5 minute run, all passing.# Please enter the commit message for your changes. Lines starting

Provide non-dirty-scheduler variants for small strings, accurately bump
reductions for these strings.

While here, provide EQC test cases for the two functions.

Expose Seal Box functions

Implementation of detached signatures

Add bindings to the libsodium DSA operations 'crypto_sign_detached' and 'crypto_sign_verify_detached'