Ability to read ZIP and GZIP files

All methods in Readable accepting one or more File objects will see if the
file contents are compressed with ZIP or GZIP format and decompress on the
fly while reading.
Certainly, good you brought that up. I'd like to throw IOException all the way out, via `CharSeeker`. I think that's possible if we use custom means of iterating over `Readable` instances as well. I'll see to it.