Make write interval a parameter.
Make write interval a parameter.

Problem: as Dominic pointed out, flumedb is general purpose, so even if one write
every 10K messages is a good compromise for ssb, it might be problematic
for other projects.

Solution: don't do periodic writes by default, but do allow passing a
parameter to the module to set them up.

Also I guess the periodic counter condition was inverted. :P

flumedb/flumeview-reduce