Demesdraw

* Added mouseover annotation popups for interactive tubes plots.
* Dropped support for Python 3.6.
* Performance improvement when calculating tube positions.
* Fix incompatibility with "legend" labels and matplotlib 3.6.0.

* Improved the default positions of demes in `demesdraw.tubes()`
for tree-like models and more elaborate models with many demes.
The previously used optimisation procedure (scipy's SLSQP) has been
removed in favour of constrained convex optimisation using `cvxpy`.
* Increased the default amount of space that separates demes in
`demesdraw.tubes()`, and use more space when there are more
contemporary demes (see `demesdraw.utils.separation_heuristic()`).
* Filter numpy warnings about overflow when using a log scale.
The overflow in question is harmless and these warnings only serve
to confuse users.

**Breaking change**

* Removed the `optimisation_rounds` parameter to `demesdraw.tubes()`.

**Breaking change**

* Updates for demes 0.2.0, which changes the syntax for pulses
from using a single `source` and `proportion` to using a list of
`sources` and a list of `proportions`.

* Added `max_time` parameter to `demesdraw.tubes()`.
* Don't draw ancestry lines for vertically stacked demes.
* Pin demes < 0.2 in install_requires.
* Made some `demesdraw.utils` functions public and cleaned up namespace.
* Added CLI, with `tubes` and `size_history` subcommands.

* Fixed problem with numpy 1.21.

* Reinstate support for Python 3.6.