Merge pull request #2317 from lambday/feature/btest

B-test MMD added
small updates to HSIC documentation
Merge pull request #2345 from sejdino/feature/mmd

small updates to HSIC documentation
Fix overflow error in statistic and variance multiplier

In CLinearTimeMMD and CBTestMMD the statistic and variance multipliers
were computed naively which caused overflow problems. Got rid of that

Changed methods are

 - CLinearTimeMMD::compute_stat_est_multiplier()
 - CLinearTimeMMD::compute_var_est_multiplier()
 - CLinearTimeMMD::compute_gaussian_multiplier()
 - CBTestMMD::compute_stat_est_multiplier()
 - CBTestMMD::compute_var_est_multiplier()
Added libshogun example for B-test MMD