Use Conan to install dependencies

.gitlab-ci.yml

CMakeLists.txt

README.md

conanfile.txt

meson.build

src/csg/CMakeLists.txt

src/csg/meson.build

src/csg/tests/CMakeLists.txt

src/csg/tests/meson.build

src/inputs/meson.build

src/inputs/tests/meson.build