Multiple inputs

Especially with file input (https://github.com/jedisct1/flowgger/issues/20), it may be desirable to merge the logs from multiple sources (each with their own decoder).

Start by reading issue #20, especially its discussion of file input, then inspect the repository's existing input and decoder entry points. The issue does not name files or tests; completion would require a decided design for merging logs from multiple sources while allowing each source to use its own decoder.

Written by the indexing model from the issue text.