command/map: add Alt/Super as aliases for Mod1/Mod4

I personally made the mistake of using Alt instead of Mod1 when messing
with my config. This change makes things a bit more user
friendly/intuitive.

doc/riverctl.1.scd

@@ -162,14 +162,17 @@ is active. It cannot be entered or exited manually.
 The following modifiers are available for use in mappings:
 
 	- Shift
-	- Lock (Caps lock)
-	- Control (Ctrl)
+	- Lock
+	- Control
 	- Mod1 (Alt)
 	- Mod2
 	- Mod3
-	- Mod4 (Super, Logo, Windows)
+	- Mod4 (Super)
 	- Mod5
-	- None (Create a mapping without modifiers)
+	- None
+
+Alt and Super are aliases for Mod1 and Mod4 respectively. None allows creating
+a mapping without modifiers
 
 Keys are specified by their XKB keysym name. See
 _/usr/include/xkbcommon/xkbcommon-keysyms.h_ for the complete list.

river/command/map.zig

@@ -187,9 +187,11 @@ fn parseModifiers(
             .{ .name = "Lock", .field_name = "caps" },
             .{ .name = "Control", .field_name = "ctrl" },
             .{ .name = "Mod1", .field_name = "alt" },
+            .{ .name = "Alt", .field_name = "alt" },
             .{ .name = "Mod2", .field_name = "mod2" },
             .{ .name = "Mod3", .field_name = "mod3" },
             .{ .name = "Mod4", .field_name = "logo" },
+            .{ .name = "Super", .field_name = "logo" },
             .{ .name = "Mod5", .field_name = "mod5" },
         }) |def| {
             if (std.mem.eql(u8, def.name, mod_name)) {