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/mainmenu.go

@@ -79,7 +79,8 @@ type mainmenuData struct {
 
 // mainmenu transaction accepts a mainmenuData struct as the data if the
 // option field or error message should be populated.
-func (sess *session) mainmenu(conn net.Conn, data any) (go3270.Tx, any, error) {
+func (sess *session) mainmenu(conn net.Conn, _ go3270.DevInfo, data any) (
+	go3270.Tx, any, error) {
 
 	fieldValues := make(map[string]string)
 
@@ -182,8 +183,8 @@ var exampleScreen = go3270.Screen{
 // exampleFeature is a transaction that will act as a placeholder for real
 // application functionality. It accepts a string in the data which will
 // be displayed on the panel.
-func (sess *session) exampleFeature(conn net.Conn, data any) (go3270.Tx,
-	any, error) {
+func (sess *session) exampleFeature(conn net.Conn, _ go3270.DevInfo,
+	data any) (go3270.Tx, any, error) {
 
 	fieldValues := make(map[string]string)