CMake package config does not reference include directory

[SamVanheer]

When using CMake's package config file to add the library to a project using find_package the include directory is not referenced, making it impossible to include mstch.hpp in your own project.

To fix this, modify src/CMakeLists.txt from this:

install(
    TARGETS mstch EXPORT mstchTargets
    LIBRARY DESTINATION lib
    ARCHIVE DESTINATION lib)

To this:

install(
    TARGETS mstch EXPORT mstchTargets
    LIBRARY DESTINATION lib
    ARCHIVE DESTINATION lib
    INCLUDES DESTINATION include)

This tells CMake to set the INTERFACE_INCLUDE_DIRECTORIES property on the target to ${CMAKE_INSTALL_PREFIX}/include, allowing you to #include <mstch/mstch.hpp>.