Use cmake's newer version of the PROJECT() function

Clean up unused variables and simplify.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9cc63d7..49d00f4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -5,7 +5,11 @@
 
 LIST(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR})
 
-PROJECT(libzip C)
+PROJECT(libzip
+  VERSION 1.6.1.1
+  DESCRIPTION "zip archive library"
+  HOMEPAGE_URL "https://libzip.org/"
+  LANGUAGES C)
 
 OPTION(ENABLE_COMMONCRYPTO "Enable use of CommonCrypto" ON)
 OPTION(ENABLE_GNUTLS "Enable use of GnuTLS" ON)
@@ -77,21 +81,7 @@
   ENDIF()
 ENDIF()
 
-SET(PACKAGE "libzip")
-SET(PACKAGE_NAME ${PACKAGE})
-SET(PACKAGE_VERSION_MAJOR "1")
-SET(PACKAGE_VERSION_MINOR "6")
-SET(PACKAGE_VERSION_MICRO "1a")
-#SET(VERSION "${PACKAGE_VERSION_MAJOR}.${PACKAGE_VERSION_MINOR}")
-SET(VERSION "${PACKAGE_VERSION_MAJOR}.${PACKAGE_VERSION_MINOR}.${PACKAGE_VERSION_MICRO}")
-SET(PACKAGE_VERSION ${VERSION})
-SET(LIBZIP_VERSION ${PACKAGE_VERSION})
-SET(LIBZIP_VERSION_MAJOR ${PACKAGE_VERSION_MAJOR})
-SET(LIBZIP_VERSION_MINOR ${PACKAGE_VERSION_MINOR})
-SET(LIBZIP_VERSION_MICRO ${PACKAGE_VERSION_MICRO})
-SET(PACKAGE_STRING "${PACKAGE_NAME} ${PACKAGE_VERSION}")
-
-SET(ARCHIVE_NAME ${PACKAGE_NAME}-${PACKAGE_VERSION})
+SET(ARCHIVE_NAME ${CMAKE_PROJECT_NAME}-${CMAKE_PROJECT_VERSION})
 IF(NOT TARGET dist)
 ADD_CUSTOM_TARGET(dist
   COMMAND git config tar.tar.xz.command "xz -c"
diff --git a/cmake-config.h.in b/cmake-config.h.in
index b830eaa..9170dff 100644
--- a/cmake-config.h.in
+++ b/cmake-config.h.in
@@ -74,8 +74,8 @@
 #cmakedefine WORDS_BIGENDIAN
 #cmakedefine HAVE_SHARED
 /* END DEFINES */
-#define PACKAGE "@PACKAGE@"
-#define VERSION "@VERSION@"
+#define PACKAGE "@CMAKE_PROJECT_NAME@"
+#define VERSION "@CMAKE_PROJECT_VERSION@"
 
 #ifndef HAVE_SSIZE_T_LIBZIP
 #  if SIZE_T_LIBZIP == INT_LIBZIP
diff --git a/cmake-zipconf.h.in b/cmake-zipconf.h.in
index 197b1c3..7ab1200 100644
--- a/cmake-zipconf.h.in
+++ b/cmake-zipconf.h.in
@@ -8,10 +8,7 @@
    based on ../cmake-zipconf.h.in.
  */
 
-#cmakedefine LIBZIP_VERSION "@PACKAGE_VERSION@"
-#cmakedefine LIBZIP_VERSION_MAJOR @PACKAGE_VERSION_MAJOR@
-#cmakedefine LIBZIP_VERSION_MINOR @PACKAGE_VERSION_MINOR@
-#cmakedefine LIBZIP_VERSION_MICRO @PACKAGE_VERSION_MICRO@
+#define LIBZIP_VERSION "${libzip_VERSION}"
 
 #cmakedefine ZIP_STATIC