Add Exiv2 namespace for exported targets

* This matches an alias target name
* Recommend using the namespaced target in the README

Signed-off-by: Ryan Friedman <ryan.friedman+github@avinc.com>

README.md

@@ -350,7 +350,7 @@ set(CMAKE_CXX_EXTENSIONS OFF)
 
 find_package(exiv2 REQUIRED CONFIG NAMES exiv2)    # search ${CMAKE_INSTALL_PREFIX}/lib/cmake/exiv2/
 add_executable(exifprint ../samples/exifprint.cpp) # Create exifprint target
-target_link_libraries(exifprint PRIVATE exiv2lib)  # link exiv2lib
+target_link_libraries(exifprint PRIVATE Exiv2::exiv2lib)  # link exiv2lib
 EOF
 $ cmake .                                          # generate the makefile
 $ cmake --build .                                  # build the code

src/CMakeLists.txt

@@ -125,6 +125,7 @@ add_library( exiv2lib
     ${PUBLIC_HEADERS}
     $<TARGET_OBJECTS:exiv2lib_int>
 )
+add_library(Exiv2::exiv2lib ALIAS exiv2lib)
 
 generate_export_header(exiv2lib
     EXPORT_MACRO_NAME EXIV2API
@@ -300,7 +301,7 @@ install(FILES
 
 install(EXPORT exiv2Export 
     DESTINATION "${CMAKE_INSTALL_DATADIR}/cmake/exiv2"
-    NAMESPACE exiv2::
+    NAMESPACE Exiv2::
 )
 
 install(