update the doc
Added id3 tree pruning
add doc
Merge pull request #2121 from yorkerlin/develop

add document for the helper function at Math.h
Minor fixes in decision tree notebook
Merge pull request #2131 from iglesias/develop

Minor fixes in decision tree notebook
sudoku recognizer notebook add to news
	- accented vowels
changes in decision tree pruning method
Merge pull request #2132 from ahcorde/sudoku_ipythonNotebook

sudoku recognizer notebook add to news
minor change in prune_tree documentation
Merge pull request #2128 from mazumdarparijat/decision_tree

Added id3 tree pruning
improved gradient descent in CNeuralNetwork