GitLab

* [ci] [C++] drop support for Visual Studio 2015 (fixes #6803)

* update more references

* [ci] some additional changes to drop VS2015 and make it work from solution file (#7046)

* Update LightGBM.vcxproj

* Update LightGBM.vcxproj.filters

* Update Installation-Guide.rst

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

* add debug mode in camke

* add debug dll

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

* fix naming

* Apply suggestions from code review

* Apply suggestions from code review

* Update LightGBM.sln

* refine

* run MPI job in debug mode

* document USE_DEBUG and USE_TIMETAG
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* fix travis badge

* updated GitHub Microsoft URL