Define CMake target Boost::gil in CMakeLists.txt

Could you please add a (interface library) cmake target for gil, that specifies the include directory and dependencies.

E.g something like:

add_library(boost_gil INTERFACE)
target_include_directories(boost_gil INTERFACE include)
target_compile_options(boost_gil INTERFACE include ...)
add_library(Boost::gil ALIAS boost_gil)

target_link_libraries(boost_gil INTERFACE
Boost::filesystem
Boost::boost
JPEG::JPEG
PNG::PNG
TIFF::TIFF
)

Cmake targets depending on Boost.Gil (like your examples and test, or a user progam doing a `add_subdirectory(libs/gil)`) could then just use `target_link_libraries( my_exec Boost::gil)` and automatically get all the relevant information like include directory, transitive dependencies and any required compilation flags.