Genieclust

* [GENERAL] A paper on the `genieclust` package is now available:
M. Gagolewski, genieclust: Fast and robust hierarchical clustering,
SoftwareX 15, 100722, 2021, DOI:
[10.1016/j.softx.2021.100722](https://doi.org/10.1016/j.softx.2021.100722).

* [Python] `plots.plot_scatter` now uses a more accessible default palette
(from R 4.0.0).

* [Python and R] New function: `devergottini_index`.

* [R] Use `mlpack` instead of `RcppMLPACK` (72).
This package is merely suggested, not dependent upon.

* [Python] Require Python >= 3.7 (implied by `numpy`).

* [Python] Require `nmslib`.

* [R] Use `RcppMLPACK` directly; remove dependency on `emstreeR`.

* [R] Use `tinytest` for unit testing instead of `testthat`.

* [BUGFIX] [R] Fix build errors on Solaris.

* [BUGFIX] [Python] Add code coverage CI. Fix some minor inconsistencies.
Automate the `bdist` build chain.

* [R] Update DESCRIPTION to meet the CRAN policies.

* [BUGFIX] [Python] Fix broken build script for OS X with no OpenMP.