Add context menu for current location

Add a new boolean option herecmd_menu. If this is on, and using
a windowport that supports mouse, clicking on your character pops
up a menu of actions doable in that location. Basically this is
nothing new, as almost all of the same actions were done before
on the mouse click.

You can also pop up the context menu with the #herecmdmenu
extended command

src/options.c

@@ -129,6 +129,7 @@ static struct Bool_Opt {
     { "fullscreen", &iflags.wc2_fullscreen, FALSE, SET_IN_FILE },
     { "goldX", &iflags.goldX, FALSE, SET_IN_GAME },
     { "help", &flags.help, TRUE, SET_IN_GAME },
+    { "herecmd_menu", &iflags.herecmd_menu, FALSE, SET_IN_GAME },
     { "hilite_pet", &iflags.wc_hilite_pet, FALSE, SET_IN_GAME }, /*WC*/
     { "hilite_pile", &iflags.hilite_pile, FALSE, SET_IN_GAME },
     { "hitpointbar", &iflags.wc2_hitpointbar, FALSE, SET_IN_GAME }, /*WC2*/