copyright year update in the source header

include/curl/curl.h

include/curl/easy.h

include/curl/mprintf.h

include/curl/multi.h

include/curl/stdcheaders.h

include/curl/types.h

lib/arpa_telnet.h

lib/base64.c

lib/base64.h

lib/connect.c

lib/connect.h

lib/content_encoding.c

lib/content_encoding.h

lib/cookie.c

lib/cookie.h

lib/dict.c

lib/dict.h

lib/easy.c

lib/escape.c

lib/escape.h