Move to the modern CMake project version option

This replaces the manual ad-hoc version variables we have used since
CMake 2.x (and GLFW 2.x lite).

src/CMakeLists.txt

@@ -95,7 +95,7 @@ endif()
 add_library(glfw ${glfw_SOURCES} ${glfw_HEADERS})
 set_target_properties(glfw PROPERTIES
                       OUTPUT_NAME ${GLFW_LIB_NAME}
-                      VERSION ${GLFW_VERSION}
+                      VERSION ${GLFW_VERSION_MAJOR}.${GLFW_VERSION_MINOR}
                       SOVERSION ${GLFW_VERSION_MAJOR}
                       POSITION_INDEPENDENT_CODE ON
                       FOLDER "GLFW3")

src/glfw3.pc.in

@@ -5,7 +5,7 @@ libdir=@CMAKE_INSTALL_FULL_LIBDIR@
 
 Name: GLFW
 Description: A multi-platform library for OpenGL, window and input
-Version: @GLFW_VERSION_FULL@
+Version: @GLFW_VERSION@
 URL: https://www.glfw.org/
 Requires.private: @GLFW_PKG_DEPS@
 Libs: -L${libdir} -l@GLFW_LIB_NAME@