Dual text screen VIC bank swap

[Whammo]

Adds an additional text screen at VIC bank 2

 56576 constant port
 53272 constant vbase
 648   constant scre
     1 value done
 port c@ constant porta
 vbase c@ constant vbasea
 scre c@ constant screa

: bank
porta 252 and 1 or port c!
5 vbase c! 128 scre c!
14 emit done if page then ;

: back 0 to done
 porta port vbasea vbase screa scre
c! c! c! ;