Now that table size can be calculated, lets store the number of entries
instead of size in the header so we can rely on that when reading
entries, instead of the actual size on disk. this is safer if data is
appended to the file outside of the application.
Somehow I apperently missed to do linear probing in he_insert that
results in colliding entries read from file (and when resizing)
to be dropped on the floor.
Lets not drop things on the floor anymore, certainly there is
another place in the table that will do fine instead of just
giving up and throw it on the floor.
use sha1 hashes instead of c-strings to make records fixed size.
because it's hard to find collisions in sha1 hashes, this works well
in practise. And dynamic memory allocation for the variadic size keys
is not needed anymore. space is also reduced due to most key strings being
more than 20 bytes long.
calculating sha1 should be fast enough to not make any more overhead
than dynamic memory allocation did.
