CmakeLists.txt: add INSTALL_NAME_DIR property for target hqr

Needed on macOS, otherwise at *execution* you get a message like:

dyld: Library not loaded: @rpath/libhqr.0.1.0.dylib
  Referenced from: ***your executable name here***
  Reason: image not found
Abort trap: 6

src/CMakeLists.txt

@@ -55,6 +55,7 @@ set_target_properties(hqr PROPERTIES VERSION ${HQR_VERSION})
 target_include_directories(hqr PUBLIC
   $<BUILD_INTERFACE:${HQR_SOURCE_DIR}/include>
   $<INSTALL_INTERFACE:include>)
+set_property(TARGET hqr PROPERTY INSTALL_NAME_DIR "${CMAKE_INSTALL_PREFIX}/lib")
 
 # Users of our library will need the header defining the API
 set_target_properties(hqr PROPERTIES PUBLIC_HEADER ${HQR_SOURCE_DIR}/include/libhqr.h)