demo/*: demos
src/CostFunc.py, src/FeedforwardNeuNet.py: add sparsity for my neural network.
testSuite/Test_FeedforwardNeuNet.py: add test cases for sparse costFunc and its gradient.
doc/conf.py: switch to mathjax.
doc/costFunc.rst: add documentation for sparse costFunc and costFuncGrad.
doc/deepArchitecture.rst: update nn architectural figure.
doc/demo.rst: add sparse autoencoder demo.
Merge branch 'dev/src'

Conflicts:
	demo/Kaggle_digits_recognition.ipynb
Merge branch 'dev/doc'