Added MLE for 'Bernoulli' distribution
Removed redundant type in 'Sample.Summary.Monoid'
Added 'Summary.moment' which returns i-th sample moment
Added 'MME' sub-signature

  MME allows to estimate distribution parameters from a given sample
  using method of moments
Moved moment calculation to 'Sample', see description of 'Sample.moments' for details
Added OPAM package stub for the upcoming release
Cleaned up signatures in 'Distributions'

  - Removed 'MLE' and 'MME', because they are useless in the generic
    case, i. e. estimating parameters of some abstract distribution
  - Merged 'Features' and 'FeaturesOpt'
Added MMEs for all distributions except two

  - 'Cauchy' distribution, no moments -- no estimate
  - 'Hypergeometric' distribution, Wolfram Alpha failed to compute these
    in the time provided for unregistered users :(
Updated 'CHANGES'
Added MLE for 'Categorical' distribution
Switched to drone.io CI
Generalized 'Sample.quantile' to support multiple probabilities -- closes #29
Minor documentation improvements
Fixed a nasty typo in 'Sample.iqr'
Added a simple benchmark for 'Sample.KDE'
Minor performance improvements in 'Sample.KDE' and 'Sample.histogram'
Cleaned up 'Resampling' and 'Internal'
Okay, we don't really need these benchmarks (at least atm)
Switched to 'StdLabels' everywhere
More cleaning up 'Internal'

  - Moved 'range' and 'reorder' to 'Base'
  - Added labels to 'Matrix_flat' functions