Add create API

[akalin]

Add create API for #6.

[akalin]

@brenthuisman what do you think of this API for creating a par2 file? (take a look at main.go) would you be able to use it?

[brenthuisman]

Looks good! The EncoderDelegate seems optional (it'll default when set to nil). Is there any use-case where a library consumer might want/need to set this?

[akalin]

The default delegate logs to stdout/stderr, which libraries shouldn't do in general (IMO), unless there's some way to turn it off.

Is the default logging behavior desired for your use case? If not, I might just make the default not log at all.

[brenthuisman]

By default I intercept stdout and stderr and route to /dev/null.

[akalin]

Ah cool, I'll set it to not log by default, then.