emile: API break, rename sha1 to hmac_sha1, introduce real sha1.

emile: API break, rename sha1 to hmac_sha1, introduce real sha1.

emile_binbuf_sha1() was actually doing HMAC version using the given
key. This doesn't work when all you need is just the SHA1 of the input
data.

Then rename emile_binbuf_sha1() to emile_binbuf_hmac_sha1() and
introduce a new version without key/keylen.

This API was marked as BETA and no real users in the codebase, then it
shouldn't cause us problems.