FindJsonCpp: add version detection

CMake/FindJsonCpp.cmake

@@ -19,8 +19,21 @@ find_library(JsonCpp_LIBRARY
 set(JsonCpp_INCLUDE_DIRS ${JsonCpp_INCLUDE_DIR})
 set(JsonCpp_LIBRARIES "${JsonCpp_LIBRARY}")
 
+set(_JsonCpp_version_args)
+if (EXISTS "${JsonCpp_INCLUDE_DIR}/json/version.h")
+  file(STRINGS "${JsonCpp_INCLUDE_DIR}/json/version.h" _JsonCpp_version_contents REGEX "#\\s+define\\s+JSONCPP_VERSION_[A-Z]+")
+  foreach (_JsonCpp_version_part MAJOR MINOR PATCH)
+    string(REGEX REPLACE ".*#\\s*define ARMA_VERSION_${_JsonCpp_version_part}\\s+([0-9]+).*" "\\1" JsonCpp_VERSION_${_JsonCpp_version_part} "${_JsonCpp_version_contents}")
+  endforeach ()
+
+  set(JsonCpp_VERSION_STRING "${JsonCpp_VERSION_MAJOR}.${JsonCpp_VERSION_MINOR}.${JsonCpp_VERSION_PATCH}")
+
+  set(_JsonCpp_version_args VERSION_VAR JsonCpp_VERSION_STRING)
+endif ()
+
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args(JsonCpp DEFAULT_MSG
-  JsonCpp_LIBRARIES JsonCpp_INCLUDE_DIRS)
+  JsonCpp_LIBRARIES JsonCpp_INCLUDE_DIRS
+  ${_JsonCpp_version_args})
 
 mark_as_advanced(JsonCpp_INCLUDE_DIR JsonCpp_LIBRARY)