Add (commented out) target to build static library with cmake.

Not enabled since it doubles the compilation time and not everyone
will need it.

From Keith Jones <keith@keithjjones.com>.
diff --git a/THANKS b/THANKS
index 5fb5b2f..7a65068 100644
--- a/THANKS
+++ b/THANKS
@@ -23,6 +23,7 @@
 Jan Weiß <jan@geheimwerk.de>
 Joel Ebrahimi <joel.ebrahimi@gmail.com>
 Jono Spiro <jono.spiro@gmail.com>
+Keith Jones <keith@keithjjones.com>
 Kohei Yoshida <kohei.yoshida@gmail.com>
 Leith Bade <leith@mapbox.com>
 Lubomir I. Ivanov <neolit123@gmail.com>
diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 2a0962f..feebb62 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -191,3 +191,11 @@
   ARCHIVE DESTINATION lib
   LIBRARY DESTINATION lib)
 #CREATE_LIBTOOL_FILE(zip lib)
+
+#ADD_LIBRARY(zipstatic STATIC ${LIBZIP_SOURCES} ${LIBZIP_EXTRA_FILES} ${LIBZIP_OPSYS_FILES})
+#SET_TARGET_PROPERTIES(zipstatic PROPERTIES VERSION 3.0 SOVERSION 3 )
+#TARGET_LINK_LIBRARIES(zipstatic ${ZLIB_LIBRARY})
+#INSTALL(TARGETS zipstatic
+#  RUNTIME DESTINATION bin
+#  ARCHIVE DESTINATION lib
+#  LIBRARY DESTINATION lib)