Added ex91 - closing in on async!

exercises/091_async8.zig

@@ -0,0 +1,35 @@
+//
+// You have doubtless noticed that 'suspend' requires a block
+// expression like so:
+//
+//     suspend {}
+//
+// The suspend block executes when a function suspends. To get
+// sense for when this happens, please make the following
+// program print the string
+//
+//     "ABCDEF"
+//
+const print = @import("std").debug.print;
+
+pub fn main() void {
+    print("A", .{});
+
+    var frame = async suspendable();
+
+    print("X", .{});
+
+    resume frame;
+
+    print("F", .{});
+}
+
+fn suspendable() void {
+    print("X", .{});
+
+    suspend {
+        print("X", .{});
+    }
+
+    print("X", .{});
+}