+ Refactor classification.py to enable profiling.
+ Fix a bug caused by memory optimizing.
+ Change the dtype to float32 to save some memory
+ Enable multi-layer Fredholm kernel, change the config file correspondingly.
+ Add a few functions for profiling.
+ Modify tsvm.py to allow sparse input.
+ Modify l2_kernel_classifier.py to deal with the issue of inversing a matrix with inf condition number.
+ Refactor laprlsc.py to reuse the code from l2_kernel_classifier.py