Listing does not show value of EQU or RS

[sikthehedgehog]

When defining an equ or rs label, the listing still shows the current PC value in its place. Since one of the most useful features of a listing is to be able to see where everything is, this may be a problem if somebody wants to see what value was computed (especially if it's intended to be an address in ROM or RAM, as you may not know where that ended up).

The suggestion would be to show the computed value instead of PC when the line defines a permanent label (in the case of rs, this also involves issue #13).

Note: this wouldn't apply to temporary labels (those that can change over time) or stuff like macros, as in those cases it's impossible to determine what value they're supposed to have.