* Database.cs:
* BrainBackend.cs:
* BrainFrontend.cs: Move sentence rarity calculation into
  BrainFrontend.

* Chainey.cs: Modify diagnostics output.
* BrainFrontend.cs: Shuffle some code around, and make Filter a
  property instead of a paramter.

* Chainey.cs: Filter is now a property, so make the appropriate
  changes.

* Database.cs: Allow whitespace-only "words", to grant callers the
  freedom to split on whatever whitespace (but at least space) they
  want.
Making preparations for allowing Chainey to respond randomly to
unaddressed sentences spoken in 'Learning' channels.
Implement Sentence.ToString
Version bump and code shuffle.