GitLab

* [ci] upgrade actions/checkout to v2.4.0

* re-create GITHUB_WORKSPACE

* dont update cuda

* actually revert cuda

* [R-package] use C++ compiler for pre-compile checks on Windows

* install Matrix in valgrind test

* Add {Matrix} in more places in CI and docs

* use CXX11

* use flags specific to C++11

* missing backtick
Co-authored-by: Nikita Titov <nekit94-12@hotmail.com>

* [ci] parallelize R package installs in CI jobs

* build 2

* build 3

* add ncpus in static_analysis

* start supporting Python 3.9

* Update .vsts-ci.yml

* Update .vsts-ci.yml

* Update .appveyor.yml

* Update .vsts-ci.yml

* Update .appveyor.yml

* fixed conflicts

* continue

* [ci] Move check-docs and lint jobs off Travis

* Apply suggestions from code review
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* try moving check-docs into a containerized job

* add install flag and README badge

* trying to find the error

* ignore pipefail

* remove -e

* Apply suggestions from code review
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* more changes

* additional changes

* Update .github/workflows/static_analysis.yml

* Update README.md
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* move constants
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>