Problems using CMake on Windows
Hello,

I'm having trouble getting glad working with CMake on Windows. I would like to have glad run as part of our CMake build process, and use the generated glad.h/lib files in our project.

For testing, my folder structure looks like:
`C:\Users\me\projects\glad`        (cloned from GitHub)
`C:\Users\me\projects\glad-driver` (new directory with nothing except a CMakeLists.txt)

I made empty `build\` directories off of each of these as well.

The contents of `glad-driver\CMakeLists.txt` are:
```
cmake_minimum_required(VERSION 3.0)
set(glad_DIR "..\\glad\\build")
find_package(glad REQUIRED)
```
Here are the commands I use to try to build glad-driver. First run CMake on glad:

>\> cd glad\build
>\> cmake -DGLAD_INSTALL=ON ..

Result:

>-- Building for: Visual Studio 15 2017
>-- The C compiler identification is MSVC 19.15.26729.0
>-- Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.15.26726/bin/Hostx86/x86/cl.exe
>-- Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.15.26726/bin/Hostx86/x86/cl.exe -- works
>-- Detecting C compiler ABI info
>-- Detecting C compiler ABI info - done
>-- Detecting C compile features
>-- Detecting C compile features - done
>-- Found PythonInterp: C:/Users/me/AppData/Local/Programs/Python/Python36/python.exe (found version "3.6.5")
>-- Configuring done
>-- Generating done
>-- Build files have been written to: C:/Users/me/projects/glad/build

Next, compile the generated Visual Studio projects:

>\> msbuild /p:Configuration=Release ALL_BUILD.vcxproj

Result:
(Lots of stuff then):

>Done Building Project "C:\Users\me\projects\glad\build\ALL_BUILD.vcxproj" (default targets).
>
>Build succeeded.
>    0 Warning(s)
>    0 Error(s)
>
>Time Elapsed 00:00:02.08

Last step, try finding glad with CMake’s `find_package` command:

>\> cd ..\..\glad-driver\build
>\> cmake ..

Result:
>-- Building for: Visual Studio 15 2017
>-- The C compiler identification is MSVC 19.15.26729.0
>-- The CXX compiler identification is MSVC 19.15.26729.0
>-- Check for working C compiler: C:/Program Files (x86)/Microsoft Visual >Studio/2017/Community/VC/Tools/MSVC/14.15.26726/bin/Hostx86/x86/cl.exe
> -- Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.15.26726/bin/Hostx86/x86/cl.exe -- works
> -- Detecting C compiler ABI info
> -- Detecting C compiler ABI info - done
> -- Detecting C compile features
> -- Detecting C compile features - done
> -- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.15.26726/bin/Hostx86/x86/cl.exe
> -- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.15.26726/bin/Hostx86/x86/cl.exe -- works
> -- Detecting CXX compiler ABI info
> -- Detecting CXX compiler ABI info - done
> -- Detecting CXX compile features
> -- Detecting CXX compile features - done
> CMake Error at C:/Users/me/projects/glad/build/gladConfig.cmake:27 (include):
>   include could not find load file:
> 
>     C:/Users/me/projects/glad/build/gladTargets.cmake
> Call Stack (most recent call first):
>   CMakeLists.txt:3 (find_package)
> 
> -- Configuring incomplete, errors occurred!
> See also "C:/Users/me/projects/glad-driver/build/CMakeFiles/CMakeOutput.log".
> 

Further investigation reveals that the gladTargets.cmake file (and a bunch couple of seemingly related files are *actually* located at):

`C:\Users\me\projects\glad\build\CMakeFiles\Export\lib\cmake\glad\gladTargets.cmake`

I don’t know why `gladConfig.cmake` ends up in `build` and `gladTargets.cmake` ends up in `build\CmakeFiles\Export\lib\cmake\glad`.

If I copy `gladTargets.cmake` into the `glad\build` directory and re-run CMake from glad-driver, then my glad-driver CMake project does succeed. However if I add the following lines to glad-driver\CMakeLists.txt:

```
add_executable (hello_glad "HelloGlad.cpp")
target_link_libraries(hello_glad glad::glad)
```
then I get the following error:

> CMake Error in CMakeLists.txt:
>   Imported target "glad::glad" includes non-existent path
> 
>     "C:/Users/me/include/glad"
> 
>   in its INTERFACE_INCLUDE_DIRECTORIES.  Possible reasons include:
> 
>   * The path was deleted, renamed, or moved to another location.
> 
>   * An install or uninstall procedure did not complete successfully.
> 
>   * The installation package was faulty and references files it does not
>   provide.


Any help would be greatly appreciated!

