prepare for new release: 2021-04-15

[strega-nil]

The following PRs are included:

• hopefully fix crash in constraints (hopefully fix crash in constraints #60)
• [vcpkg] allow --version to check the version ([vcpkg] allow --version to check the version #50)
• Remove baseline warning (Remove baseline warning #27)
• [git] always pass autocrlf=false ([git] always pass autocrlf=false #58)
• ignore QtCreator CMake project files (ignore QtCreator CMake project files #54)
• ignore .DS_store files (ignore .DS_store files #53)
• [vcpkg] x-add-version now also checks if the manifest file is properly formatted ([vcpkg] x-add-version now also checks if the manifest file is properly formatted #43)
• hopefully fix ci issue #16773 (hopefully fix ci issue #16773 #34)
• Add docs to set VCPKG_ROOT to run tests (Add docs to set VCPKG_ROOT to run tests #45)
• [vcpkg] x-add-version improve speed by calling get_builtin_baseline only once ([vcpkg] x-add-version improve speed by calling get_builtin_baseline only once #44)
• add clang-format version to format-cxxcode (add clang-format version to format-cxxcode #41)
• [vcpkg] Introduce experimental workaround X_VCPKG_NUGET_ID_PREFIX ([vcpkg] Introduce experimental workaround X_VCPKG_NUGET_ID_PREFIX #40)
• [supports] Add native identifier expression and x-check-support command ([supports] Add native identifier expression and x-check-support command #29)
• [metrics] Split reporting of installs into name:triplet ([metrics] Split reporting of installs into name:triplet #39)
• [vcpkg] Improve error when accessing missing feature ([vcpkg] Improve error when accessing missing feature #38)
• [vcpkg] Allow shallow git registries (Allow shallow git registries #37)
• Disable git autocrlf when archiving tree (Disable git autocrlf when archiving tree #36)
• Use only named packages from extra registries (Use only named packages from extra registries #35)
• [registries] add metrics ([registries] add metrics #30)
• Add vcpkg policy cmake helper port support (Add vcpkg policy cmake helper port support #17)
• [osx] add support for rosetta ([osx] add support for rosetta #23)
• don't build tls12-download unless it's needed (don't build tls12-download unless it's needed #33)
• Add new telemetry points for versioning ([metrics] Add new telemetry points for versioning #21)
• add cmake_minimum_required to vcpkg_tags (add cmake_minimum_required to vcpkg_tags #25)
• [x-add-versions] Perform atomic replacement of versioning files ([x-add-versions] Perform atomic replacement of versioning files #28)
• [tools] support gsutil ([tools] support gsutil #19)
• add CUDA 11.1 and 11.2 to KEEP_ENV_VARS defaults (Add CUDA 11.1 and 11.2 to KEEP_ENV_VARS defaults #26)
• Add finite timeout on CURL metrics endpoint. (Fix CURL filesystem deadlock with corporate proxy #22)
• fix UB in make_error_code(utf8_errc) (fix UB in make_error_code(utf8_errc) #18)