espeak backend should raise OutputError on init failure

[tyrylu]

Hello. When i was trying to add additional Linux output, i noticed that the espeak one raises RuntimeError on failure and such crashes the entire stack when the output autodiscovery runs. It should probably raise an OutputError too. By the way, how did it come to the situation that the ctoth's fork is on pypi and if it is the official one, should not the ownership be transferred (because for some reason the fork accepts PRs only).