Use lager_trunc_io:format() for all messages submitted via
lager:log().  Also, refactor list flattening and final newline
stripping into shared func that uses re:replace() to do both.

Fixed syntax error w.r.t. configuration example

If backends have a failure or something, don't discard the messages,
wait half a second and then try sending them again.

This solves an issue reported by 'cloudhead' in IRC where deep lists
weren't being flattened when printed with format specifiers like ~s ~p
and ~P, all of which should flatten the list.

Adt add simple rotation

IBM punchcards rejoice! Basho supports your right to continue to affect
how we format source code :)

Adding date spec parsing and calculation of when a spec indicates a file
next needs to be rotated.

az558