Added Logarithmic Naive Bayes Learner. (aimacode#928)

* test case for zebra problem

* Revert "Merge remote-tracking branch 'upstream/master'"

This reverts commit 5ceab1a, reversing
changes made to 34997e4.

* discarded HEAD changes for merge

* added ensemble_learner jpeg

* updated travis and search

* Added logarithmic learner in nlp_apps (aimacode#890)

* Remove zebra tests

* revised Bayes learner explanation

* added missing SimpleReflexAgent from upstream

Author: dsaw