When you build and install `libde265` with CMake, you cannot properly use the library after using `target_link_libraries`, because the include directories are not propagated properly.

The reason is this line:
https://github.com/strukturag/libde265/blob/0b1752abff97cb542941d317a0d18aa50cb199b1/libde265/CMakeLists.txt#L132

You also need to state where the header files can be found in the installed case, for an example like this:
https://github.com/eclipse-ecal/tcp_pubsub/blob/4ceafb6b55ce41149ed9473dae7e8ea37235a3cc/tcp_pubsub/CMakeLists.txt#L96-L103

Sample CMakeLists.txt file to use libde265:
```
cmake_minimum_required(VERSION 3.15)
project(libde265PackageTest CXX)

find_package(libde265 REQUIRED)
add_executable(libde265_test libde265_test.cpp)
target_link_libraries(libde265_test PRIVATE  de265)
```
Building a sample then fails:  
```
fatal error: de265-version.h: No such file or directory
```


Would you accept a PR to address this issue?
At the same time I would recommend to export targets into a namespace so they can be linked with `libde265::libde265`, to make clear to CMake that this target is imported and then it gets better diagnostics if it cannot be found.
CMake: include directories not propagated with target
This is a GitHub Issue
repo:libde265
owner:strukturag
Title : CMake: include directories not propagated with target
Issue date:

--- start body ---
When you build and install `libde265` with CMake, you cannot properly use the library after using `target_link_libraries`, because the include directories are not propagated properly.

The reason is this line:
https://github.com/strukturag/libde265/blob/0b1752abff97cb542941d317a0d18aa50cb199b1/libde265/CMakeLists.txt#L132

You also need to state where the header files can be found in the installed case, for an example like this:
https://github.com/eclipse-ecal/tcp_pubsub/blob/4ceafb6b55ce41149ed9473dae7e8ea37235a3cc/tcp_pubsub/CMakeLists.txt#L96-L103

Sample CMakeLists.txt file to use libde265:
```
cmake_minimum_required(VERSION 3.15)
project(libde265PackageTest CXX)

find_package(libde265 REQUIRED)
add_executable(libde265_test libde265_test.cpp)
target_link_libraries(libde265_test PRIVATE  de265)
```
Building a sample then fails:  
```
fatal error: de265-version.h: No such file or directory
```


Would you accept a PR to address this issue?
At the same time I would recommend to export targets into a namespace so they can be linked with `libde265::libde265`, to make clear to CMake that this target is imported and then it gets better diagnostics if it cannot be found.
--- end body ---
