add contributions to readme
Removing last memory warnings on buildbot (could not reproduce them locally).
Merge pull request #2229 from pickle27/develop

add contributions to readme
CART added
Merge pull request #2239 from mazumdarparijat/CART

CART added
extended neuralnets to support arbitrary  acyclic graphs
added obtain_from_generic method
Merge pull request #2242 from karlnapf/develop

added CANOVAKernel::obtain_from_generic
Merge pull request #2232 from tklein23/more_valgrind_suppressions

Removing last memory warnings on buildbot (could not reproduce them locally)
bug fix
clone_tree method added
Fixed a bug in factor graph ipython notebook
the base class
Merge pull request #2238 from abinashpanda/develop

Merging CStructuredOutput wrapper for MutliLabels.
Merge pull request #2249 from mazumdarparijat/CART

CTreeMachine::clone_tree() added.
bug fix
Merge pull request #2240 from khalednasr/develop

extended neuralnets to support arbitrary acyclic graphs
Updated QuadraticTimeMMD with new formulas

The previous implementation is also kept alongside with the new
implementation as DEPRECATED versions.

The changes are

 - compute_statistic method now returns m*n/(m+n)*MMD^2 estimate.
 - An incomplete estimate of statistic is made available.
 - Previous results work if statistic type is set as BIASED_DEPRECATED,
   UNBIASED_DEPRECATED which returns (m+n)*MMD^2 in general case and
   m*MMD^2 when m equals n.
 - Spectral estimate of null samples returns m*n/(m+n)*Null-samples now
   Previous method works with MMD2_SPECTRUM_DEPRECATED enum.
 - As of now gamma approximation works with DEPRECATED sets only
 - Estimate of variance of asymptotic distribution of the statistic is
   computed along with computing statistic to avoid recomputing the
   kernel. Variance under null and alternative are computed separately.
 - Similar to compute_statistic, compute_variance works with multiple
   kernels as well.
Merge pull request #2246 from yorkerlin/variational-likelihoods

the base class (VariationalLikelihood)
Merge pull request #2248 from yorkerlin/lnorm_cdf

bug fix for normal_cdf and lnormal_cdf