[SPARK-4894][mllib] Added Bernoulli option to NaiveBayes model in mllib

Added optional model type parameter for  NaiveBayes training. Can be either Multinomial or Bernoulli.

When Bernoulli is given the Bernoulli smoothing is used for fitting and for prediction as per: http://nlp.stanford.edu/IR-book/html/htmledition/the-bernoulli-model-1.html.

 Default for model is original Multinomial fit and predict.

Added additional testing for Bernoulli and Multinomial models.

Author: leahmcguire <lmcguire@salesforce.com>
Author: Joseph K. Bradley <joseph@databricks.com>
Author: Leah McGuire <lmcguire@salesforce.com>

Closes apache#4087 from leahmcguire/master and squashes the following commits:

f3c8994 [leahmcguire] changed checks on model type to requires
acb69af [leahmcguire] removed enum type and replaces all modelType parameters with strings
2224b15 [Leah McGuire] Merge pull request palantir#2 from jkbradley/leahmcguire-master
9ad89ca [Joseph K. Bradley] removed old code
6a8f383 [Joseph K. Bradley] Added new model save/load format 2.0 for NaiveBayesModel after modelType parameter was added.  Updated tests.  Also updated ModelType enum-like type.
852a727 [leahmcguire] merged with upstream master
a22d670 [leahmcguire] changed NaiveBayesModel modelType parameter back to NaiveBayes.ModelType, made NaiveBayes.ModelType serializable, fixed getter method in NavieBayes
18f3219 [leahmcguire] removed private from naive bayes constructor for lambda only
bea62af [leahmcguire] put back in constructor for NaiveBayes
01baad7 [leahmcguire] made fixes from code review
fb0a5c7 [leahmcguire] removed typo
e2d925e [leahmcguire] fixed nonserializable error that was causing naivebayes test failures
2d0c1ba [leahmcguire] fixed typo in NaiveBayes
c298e78 [leahmcguire] fixed scala style errors
b85b0c9 [leahmcguire] Merge remote-tracking branch 'upstream/master'
900b586 [leahmcguire] fixed model call so that uses type argument
ea09b28 [leahmcguire] Merge remote-tracking branch 'upstream/master'
e016569 [leahmcguire] updated test suite with model type fix
85f298f [leahmcguire] Merge remote-tracking branch 'upstream/master'
dc65374 [leahmcguire] integrated model type fix
7622b0c [leahmcguire] added comments and fixed style as per rb
b93aaf6 [Leah McGuire] Merge pull request #1 from jkbradley/nb-model-type
3730572 [Joseph K. Bradley] modified NB model type to be more Java-friendly
b61b5e2 [leahmcguire] added back compatable constructor to NaiveBayesModel to fix MIMA test failure
5a4a534 [leahmcguire] fixed scala style error in NaiveBayes
3891bf2 [leahmcguire] synced with apache spark and resolved merge conflict
d9477ed [leahmcguire] removed old inaccurate comment from test suite for mllib naive bayes
76e5b0f [leahmcguire] removed unnecessary sort from test
0313c0c [leahmcguire] fixed style error in NaiveBayes.scala
4a3676d [leahmcguire] Updated changes re-comments. Got rid of verbose populateMatrix method. Public api now has string instead of enumeration. Docs are updated."
ce73c63 [leahmcguire] added Bernoulli option to niave bayes model in mllib, added optional model type parameter for training. When Bernoulli is given the Bernoulli smoothing is used for fitting and for prediction http://nlp.stanford.edu/IR-book/html/htmledition/the-bernoulli-model-1.html

Author: leahmcguire

docs/mllib-naive-bayes.md

@@ -13,12 +13,15 @@ compute the conditional probability distribution of label given an observation
 and use it for prediction.
 
 MLlib supports [multinomial naive
-Bayes](http://en.wikipedia.org/wiki/Naive_Bayes_classifier#Multinomial_naive_Bayes),
-which is typically used for [document
-classification](http://nlp.stanford.edu/IR-book/html/htmledition/naive-bayes-text-classification-1.html).
+Bayes](http://en.wikipedia.org/wiki/Naive_Bayes_classifier#Multinomial_naive_Bayes)
+and [Bernoulli naive Bayes] (http://nlp.stanford.edu/IR-book/html/htmledition/the-bernoulli-model-1.html).
+These models are typically used for [document classification]
+(http://nlp.stanford.edu/IR-book/html/htmledition/naive-bayes-text-classification-1.html).
 Within that context, each observation is a document and each
-feature represents a term whose value is the frequency of the term.
-Feature values must be nonnegative to represent term frequencies.
+feature represents a term whose value is the frequency of the term (in multinomial naive Bayes) or
+a zero or one indicating whether the term was found in the document (in Bernoulli naive Bayes).
+Feature values must be nonnegative. The model type is selected with an optional parameter
+"Multinomial" or "Bernoulli" with "Multinomial" as the default.
 [Additive smoothing](http://en.wikipedia.org/wiki/Lidstone_smoothing) can be used by
 setting the parameter $\lambda$ (default to $1.0$). For document classification, the input feature
 vectors are usually sparse, and sparse vectors should be supplied as input to take advantage of
@@ -32,7 +35,7 @@ sparsity. Since the training data is only used once, it is not necessary to cach
 [NaiveBayes](api/scala/index.html#org.apache.spark.mllib.classification.NaiveBayes$) implements
 multinomial naive Bayes. It takes an RDD of
 [LabeledPoint](api/scala/index.html#org.apache.spark.mllib.regression.LabeledPoint) and an optional
-smoothing parameter `lambda` as input, and output a
+smoothing parameter `lambda` as input, an optional model type parameter (default is Multinomial), and outputs a
 [NaiveBayesModel](api/scala/index.html#org.apache.spark.mllib.classification.NaiveBayesModel), which
 can be used for evaluation and prediction.
 
@@ -51,7 +54,7 @@ val splits = parsedData.randomSplit(Array(0.6, 0.4), seed = 11L)
 val training = splits(0)
 val test = splits(1)
 
-val model = NaiveBayes.train(training, lambda = 1.0)
+val model = NaiveBayes.train(training, lambda = 1.0, model = "Multinomial")
 
 val predictionAndLabel = test.map(p => (model.predict(p.features), p.label))
 val accuracy = 1.0 * predictionAndLabel.filter(x => x._1 == x._2).count() / test.count()