update the doc
#2119 Add IndexFeatures to CustomKernel and add document.
dot product
sudoku recognizer notebook add to news
Cleaning #imports.  Using minimal imports for protobuf.
Moved "SGRefObject::list_memory_allocs" method from header into implementation.
Moved unimplemented methods from SGObject to implementation to remove SGIO in definition.
Merge pull request #2126 from ahcorde/sudoku_ipythonNotebook

sudoku recognizer notebook add to news
Merge pull request #2127 from tklein23/develop

Cleanup: Moving implemented methods out of header files.
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
Added guard to abort when using the broken function -- to see what will break.
improved gradient descent in CNeuralNetwork