libdxfrw.pc.in: fix expansion and include path

The include dirs are processed by cmake's configure_file since commit
3431cc6 (Fix building of pkgconfig on Windows). That means every
dollar referenced variables are expanded. But ${libdir} and
${includedir} are meant as pkgconfig variables, so should not be
expanded. Fix this by @only option of configure_file (and change all
${X} references to @x@).

And since commit 70ff2fe (Install DXFRW::dxfrw target), include
files have no version number in the path.  They reside in
/usr/include/libdxfrw/*. Fix this too by removing the version suffix.

CMakeLists.txt

@@ -94,7 +94,7 @@ add_subdirectory(dwg2dxf)
 # INSTALLATION
 set(INSTALL_CONFIGDIR ${CMAKE_INSTALL_LIBDIR}/cmake/libdxfrw)
 
-configure_file(${CMAKE_CURRENT_SOURCE_DIR}/libdxfrw.pc.in libdxfrw.pc)
+configure_file(${CMAKE_CURRENT_SOURCE_DIR}/libdxfrw.pc.in libdxfrw.pc @ONLY)
 
 install(TARGETS dxfrw
 		EXPORT libdxfrw-targets

libdxfrw.pc.in

@@ -1,10 +1,10 @@
-prefix=${CMAKE_INSTALL_PREFIX}
-exec_prefix=${CMAKE_INSTALL_PREFIX}
-libdir=|${CMAKE_INSTALL_FULL_LIBDIR}
-includedir=${CMAKE_INSTALL_FULL_INCLUDEDIR}
+prefix=@CMAKE_INSTALL_PREFIX@
+exec_prefix=@CMAKE_INSTALL_PREFIX@
+libdir=|@CMAKE_INSTALL_FULL_LIBDIR@
+includedir=@CMAKE_INSTALL_FULL_INCLUDEDIR@
 
 Name: libdxfrw
 Description: c++ library to read/write dxf files in binary and ascii form
-Version: ${PROJECT_VERSION}
+Version: @PROJECT_VERSION@
 Libs: -L${libdir} -ldxfrw
-Cflags: -I${includedir}/libdxfrw${PROJECT_VERSION_MAJOR}
+Cflags: -I${includedir}/libdxfrw