Move terminal package

fixes issue where terminal_check_notappengine.go can't access terminal
package since terminal package is in an internal package

internal/terminal/terminal_check_bsd.go

@@ -1,13 +0,0 @@
-// +build darwin dragonfly freebsd netbsd openbsd
-
-package terminal
-
-import "golang.org/x/sys/unix"
-
-const ioctlReadTermios = unix.TIOCGETA
-
-func IsTerminal(fd int) bool {
-	_, err := unix.IoctlGetTermios(fd, ioctlReadTermios)
-	return err == nil
-}
-

internal/terminal/terminal_check_unix.go

@@ -1,13 +0,0 @@
-// +build linux aix
-
-package terminal
-
-import "golang.org/x/sys/unix"
-
-const ioctlReadTermios = unix.TCGETS
-
-func IsTerminal(fd int) bool {
-	_, err := unix.IoctlGetTermios(fd, ioctlReadTermios)
-	return err == nil
-}
-