ed25519_open(): check that S < l
Not strictly required, but I don't see any downsides either.
Support overlapping input and output regions in crypto_secretbox_detached()
crypto_stream_salsa20() doesn't support overlapping input and output regions,
except when they are aliases.
Add a test for ed25519 malleability and restore traditional behavior.

If an application really requires non-malleability, ED25519_PREVENT_MALLEABILITY
can be defined to enable the check.

This might become the default behavior depending on what other implementations
are planning to do.
Avoid a conditional jump
Test box_easy with overlapping in/out.
Add a test for chacha20poly1305 with overlapping pointers
Remove dead variable and assignment
Remove S<l check.
Plan is to add is_standard()/is_canonical() instead of changing the current behavior
of the verification function. Suggested by CodesInChaos.
Make include guards consistent, and avoid reserved identifiers.
Constant-time sodium_bin2hex()
Original C# code by CodesInChaos.
Make sodium_bin2hex() slightly faster
ed25519_open(): check that S < l
Not strictly required, but I don't see any downsides either.