Alternate screen size support.

This is a relatively big new feature, which introduces small breaking changes
to the API:

 * NegotiateTelnet() now returns (DevInfo, error) instead of just error.  The
   function signature for the Tx type now has one additional DevInfo parameter.
 * RunTransactions() requires one additional parameter, the DevInfo (which is
   allowed to be nil).

Otherwise, existing behavior continues to work as-is and everything still
defaults to operating on the default 24x80 terminal size.

See example5 for a larger-terminal-aware application.

Pending some time to make sure no new bugs cropped up in this release and that
the alternate screen size support works in the wild, I anticipate this will
become the v1.0.0 release of go3270.

example4/login.go

@@ -58,7 +58,8 @@ var loginScreenRules = go3270.Rules{
 
 // login transaction accepts a string value in data if the login screen
 // should be initialized with an error message.
-func (sess *session) login(conn net.Conn, data any) (go3270.Tx, any, error) {
+func (sess *session) login(conn net.Conn, _ go3270.DevInfo,
+	data any) (go3270.Tx, any, error) {
 
 	fieldValues := make(map[string]string)
 
@@ -169,7 +170,8 @@ type newuserData struct {
 	errmsg   string
 }
 
-func (sess *session) newuser(conn net.Conn, data any) (go3270.Tx, any, error) {
+func (sess *session) newuser(conn net.Conn, _ go3270.DevInfo, data any) (
+	go3270.Tx, any, error) {
 
 	fieldValues := make(map[string]string)