Releasing 'key.sieve' and 'key.sieve2' data attachments into open source hydra project.
These data attachments keep a sieve of encountered values.
The sieve of encountered values is represented as a stack of bloom filters.
If any of the bloom filters in the current stack exceeds the target saturation value then
a new stack of bloom filters is created. The data attachment stores a list of
stacks of bloom filters because we cannot transfer elements from
the old stack of bloom filters to the new stack of bloom filters.
Merge remote-tracking branch 'upstream/master'
Merge pull request #9 from mspiegel/master

'key.sieve' and 'key.sieve2'
Merge branch 'master' of https://github.com/addthis/hydra into 4pull-mostly-harmless