The root CMakeLists doesn't export the library

[siniarskimar]

A good practice when writing a library with CMake is to export any public targets. This enables code reuse and the usage of find_package().

Currently the tortelini target isn't being exported nor installed.

We should check whenever the project is a root project (ie. "${CMAKE_SOURCE_DIR} == ${CMAKE_CURRENT_SOURCE_DIR}"), provide an install target and export it.

[Qix-]

Meh I never use find_package personally as it is usually a huge headache. I tend to just add_subdirectory directly.

Feel free to PR though. :)