Consider last instance in filter and aggregator

This fixes an issue when running the VHT classifier with prequential evaluation, where
by ignoring the last instance property in filter/aggregator, the topology exited before
evaluating all instances.
Merge pull request #112 from matthieumorel/evaluate-until-last-instance

Consider last instance in filter and aggregator
Increasing performance on sparse features using prototyping of zero-valued features

Intermediate work on zero prototypes

Signed-off-by: Olivier Van Laere <vanlaere@yahoo-inc.com>

Fixing prototype issues

Signed-off-by: Olivier Van Laere <vanlaere@yahoo-inc.com>

Adding null check to cope with prequential evaluation

Signed-off-by: Olivier Van Laere <vanlaere@yahoo-inc.com>

Adding null check for estimator request on previously unseen attribute in a given class

Signed-off-by: Olivier Van Laere <vanlaere@yahoo-inc.com>
Adding comment for smoothing factor + cleaning up imports

Signed-off-by: Olivier Van Laere <vanlaere@yahoo-inc.com>
Merge pull request #113 from ovlaere/zero-prototype

Improving performance of Naive Bayes using a prototype for zero valued features
Merge pull request #6 from yahoo/master

update