cmake: install pkgconfig file

cmake/package.cmake

   /tools/
   /vim/
 )
+
+set(PACKAGE_NAME ${PROJECT_NAME})
+set(VERSION ${PROJECT_VERSION})
+
+set(prefix ${CMAKE_INSTALL_PREFIX})
+set(exec_prefix ${CMAKE_INSTALL_PREFIX})
+set(libdir "\${exec_prefix}/lib")
+set(includedir "\${prefix}/include")
+
+configure_file(
+  ${CMAKE_CURRENT_SOURCE_DIR}/${PROJECT_NAME}.pc.in
+  ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc
+  @ONLY
+)
+
+install(
+  FILES ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc DESTINATION lib/pkgconfig
+)