Fix keys of consumer handler functions

The documentation says to use function handler keys ending in "-fn", but this code currently only recognizes the old form. This commit ensures that all keys that are used within `langohr.consumers/subscribe` can be used as a parameter.
Fix broken commit: we produce a seq of keywords, not a seq of seqs
add test to verify that  takes both versions for function handler fns
Change log update
Attribute Steffen Dienst
1.0.2
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