Renamed 'gost3411' -> 'gost'.

We only export one GOST function anyway, so shorter is better.

Signed-off-by: Sebastian Hoß <mail@shoss.de>
Added testcases for all digest algorithms.

All digests calculate hash values for the same 3 test vectors. The
expected result is stolen^H^H^H^H^H^Hkindly provided by wikipedia.

Signed-off-by: Sebastian Hoß <mail@shoss.de>