add the numerical intregation base class
add the three subclasses
class structure for CHAID added
Merge pull request #2259 from yorkerlin/variational-likelihoods

the variational base class using numerical intregation
Merge pull request #2264 from mazumdarparijat/CHAID2

class structure for CHAID added
Merge pull request #2265 from mazumdarparijat/CHAID1

chi2_cdf and fdistribution_cdf added
p-value calculations added