Python 3.8 support

This MR introduces preliminary support for Python 3.8 for the basic development tool.

Package python conflicts for:
jinja2 -> python[version='>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']
click-plugins -> python[version='>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']
sphinx_rtd_theme -> python[version='>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']
twine -> python[version='>=3.6|>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']
sphinx -> python[version='>=3.5|>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']
python-dateutil -> python[version='>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']
conda-verify=3 -> python[version='>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']
gitpython -> python[version='>=3.6,<3.7.0a0|>=3.7,<3.8.0a0|>=3|>=3.4']
pytz -> python[version='>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']
conda-build=3 -> python[version='>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']
click[version='>=7'] -> python[version='>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']

After checking, the only missing package for a python-3.8 build is conda-build. A python 3.8 environment without conda-build works.

We need to wait.

For reference, the cmdline I used:

$ conda create -n bla --dry-run --use-local python=3.8 setuptools 'black>=19' 'click>=7' click-plugins certifi docformatter pytz python-dateutil gitpython python-gitlab requests sphinx 'pyyaml>=5.1' twine lxml jinja2 termcolor psutil tabulate python-graphviz conda=4 conda-verify=3 #conda-build=3

Commenting out the last requirement makes it work. Uncommenting makes it fail.

added 6 commits

• dd92b82f...f03194cd - 4 commits from branch master
• d566fe95 - [ci] Preliminary support for python-3.8
• 1b944d95 - [ci] Fix missing build deps

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added 1 commit

• 5e1195c6 - [deps] Update python-gitlab to version 2.2.0

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Ready for merge and python-3.8 support (conda-build for py38 was just released today).

merged

mentioned in commit 1e1b3d70