setup.py: update trove classifiers

setup.py: use setuptools.find_packages()

setup.py: use version from git tag

Note to self: git-tag releases since 0.7.3 !!!

rm MANIFEST.in since handled by setuptools_scm

MNT: setup.py: add dev deps

Remove pyproject.toml and requirements.txt

We already have more versatile setup.py + setup.cfg

Add docs dependencies to setup.py

setup.py: Add project_urls, shown in PyPI sidebar

setup.py: Use SPDX license identifier

Remove doc/requirements.txt in favor of setup.extras_require

setup.py: add pytest-cov dev dependency

CI: Require pytest-xdist for 'test-code-parallel' make target

Add .github/PULL_REQUEST_TEMPLATE.md

Drop CI testing on python 3.6 -- it's EOL by end of the year.

Update README.rst CI badge

DOC: Fix error "Latexmk: Missing input file: 'tgtermes.sty' from line"

CI: Install in develop mode for Docs

Since `make -C doc doctest` is run from the project dir,
sphinx/Python may import the curdir skopt instead of the
installed one.

Install in develop mode to get skopt/_version.py file created.
The alternative would be to cd elsewhere before running make.

Remove media dir; use intro image from doc/image/bo-objective.png

DOC: Merge and extend README/Development into CONTRIBUTING.md

Point docs/development to CONTRIBUTING.md as the canonical source

To v0.22.* -- it was released in 2019.
Also this joblib/joblib#917 (comment)

Futher bump tested scikit-learn == 0.24.* -- it is old enough!

The alternative would be to pin equally ancient scipy to
avoid error:

> AttributeError: 'str' object has no attribute 'decode'

The test was "rediscovered" (in a failing state) by
renaming the test case that follows it.

np.int has been deprecated so changed to int

FIX numpy int