Attempt to fix #63.
Fix AltGr key.

Iterate on keys pressed instead of chars

Only the unix implementation works.
The windows impl does not even compile...

Parametrize Editor by the Completer type

This allows the `Editor` to implement `Sync` as long as it contains a completer which implement `Sync`. It lets the `Editor` take ownership of the completer.

And do not ignorespace by default.
And do not panic when the history is empty

Make History ignore space/dups configurable (#50)