implement a new hashing scheme

This changes the hashing scheme completely. Ketama is no longer used.
Instead a consistent hashing strategy using murmur hash is used.
Additionally, the only external dependency is now libev -- the glib
dependency is removed (since there is no longer a need for GHashTable
objects) and the openssl dependency is removed (since murmur hash is
implemented natively).

This should be MUCH faster than before, because there's a faster string
hashing function, and no GLib hash objects need to do -- keys are hashed
directly to a backing tcpclient object.

I've added some tests.

Note that this uses a totally different config format.