update keymap
Run new clients in a new process session

When running a terminal emulator containing a kakoune client,
it used to still have the server tty as controlling termnal,
and so received SIGINT's from the user in it. Termnal emulators
then responded by exiting. This is no longer the case.
Fix select_next_match that would select the end of the buffer in some circumstances
Add automatic completion display in prompt mode

Controlled by the autoshowcompl option
Completers now take a CompletionFlag parameter, used to specify
we want fast completion (tag completion can be slow, we do not
want to run it if not explicitely wanted by the user).