Update CMake usage to enable C++17 (#156)

The target_compile_features command allows setting PUBLIC compile features for the library, making it implicit for the applications linking it. This reduces the CMake boilerplate required to set up a dependent project (eg. ftxui-starter).

examples/dom/CMakeLists.txt

@@ -1,7 +1,6 @@
 function(example name)
   add_executable(${name} ${name}.cpp)
   target_link_libraries(${name} PUBLIC dom)
-  set_property(TARGET ${name} PROPERTY CXX_STANDARD 17)
 endfunction(example)
 
 example(border)