feat(naivebayes): implement NaiveBayes algorithm

feat(example): a document classifier using NaiveBayes over reuters data

examples/naivebayes-doc-classifier.hs

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+module Main
+  where
+    import Sibe
+    import Sibe.NaiveBayes
+    import Text.Printf
+    import Data.List
+    import Data.Maybe
+    import Debug.Trace
+
+    main = do
+      dataset <- readFile "examples/naivebayes-doc-classifier/data-reuters"
+      test <- readFile "examples/naivebayes-doc-classifier/data-reuters-test"
+
+      classes <- map (filter (/= ' ')) . lines <$> readFile "examples/naivebayes-doc-classifier/data-classes"
+
+      let intClasses = [0..length classes - 1]
+          documents = createDocuments classes dataset
+          testDocuments = createDocuments classes test
+          nb = initialize documents
+
+      let testResults (Document text c) =
+            let r = determine text nb intClasses documents
+            in trace (classes !! c ++ " ~ " ++ classes !! r) c == r
+
+      let results = map testResults testDocuments
+
+      putStr "Accuracy: "
+      putStr . show . round $ (genericLength (filter (==True) results) / genericLength results) * 100
+      putStrLn "%"