v0.9.0

What's Changed

• [pre-commit.ci] pre-commit autoupdate by @pre-commit-ci[bot] in #179
• Use yardl 0.6.6 by @KrisThielemans in #183
• remove xtensor version upper bound, set howardhinnant_date upper bound by @KrisThielemans in #184
• [pre-commit.ci] pre-commit autoupdate by @pre-commit-ci[bot] in #185
• create C++ library and CMake export by @NikEfth and @KrisThielemans in #186
• Use yardl 0.6.7 by @KrisThielemans in #187

Full Changelog: v0.8.1...v0.9.0