Find better way to specify input

[marcverhagen]

We are quite unhappy with source=X as an option. May want to introduce format=X with X in [xml, text, ttk] and another option, but naming is tricky (genre?, domain? input-type?) and there are interactions between format/domain and what processing has already been done.

Related to #14 and #18.

[marcverhagen]

With the LIF format added (see issue #88) we have seemingly also added an inconsistency in that TTK always creates TTK except when the input is LIF as indicated by --source=lif.

It is probably better to use two parameters:

1. Use --input-format to avoid or overrule guessing of what the input format is. This can also be used to deal with the issue we have with the --pipe parameter which makes the guess currently impossible (issue Guessing the source breaks when --pipe is used #71).

2. Use --output-format to overrule the ttk default.

This doesn't solve the problem of potentially wanting to write domain specific code, but we can deal with that if needed by adding a --domain parameter.