Update CMake code for installing target

[prateek9623]

The old "install" target was working poorly in windows.
Now able to include curlcpp using find_package or FetchContent

[JosephP91]

Hi @prateek9623 I just tried your changes, and they breaks the build on linux:

CMake Error: File /home/giuseppe/Desktop/curlcpp/cmake/curlcppConfig.cmake.in does not exist.
CMake Error at /usr/share/cmake-3.16/Modules/CMakePackageConfigHelpers.cmake:330 (configure_file):
  configure_file Problem configuring file
Call Stack (most recent call first):
  CMakeLists.txt:48 (configure_package_config_file)

[prateek9623]

I tried building in a docker container and it is building successfully, but still, I looked in my changes and found a typo. Maybe that was the issue can you retry building it.

[JosephP91]

Confirmed! Great!