Add docs and use default value for hasher names.
Make hashers serializable.

There exists still a small bug that I could not find; the unit test
istate/opaque.bro fails. If someone sees why, please chime in.
Merge remote-tracking branch 'origin/master' into topic/matthias/bloom-filter

Conflicts:
	src/probabilistic/Hasher.h
Update submodules.
Merge remote-tracking branch 'origin/topic/matthias/bloom-filter'

* origin/topic/matthias/bloom-filter:
  Update submodules.
  Make hashers serializable.
  Add docs and use default value for hasher names.
Updating submodule(s).

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