X3270/APL support

Description
x3270 supports both display and input of APL characters.

Display
The  font includes a full set of APL characters; the other 3270 fonts have subsets (mostly the line-drawing characters from code page 310 ). Many  (Unicode) fonts have the most or all of the APL characters, except for the underlined alphabetics, which are not standard Unicode characters.

Input
In the default keymap, the key combination Shift-Escape performs the following functions: In the temporary keymap, Shift-Escape is changed to undo these three functions.
 * Enables APL mode for paste operations.
 * Sets a temporary keymap to allow APL characters to be entered.
 * Sets a temporary compose map to allow APL characters to be entered.

APL temporary compose map
Symbols marked Sharp come from Sharp APL and are not on code page 310.