implemented return instruction; Fixed Bug in Stack.pop() (#4)

Co-authored-by: Darkress <30271678+DarkressX@users.noreply.github.com>
Reviewed-on: darkress/pic16f84-sim#4

de/darkress/pic16f84sim/commands/Return.java

@@ -0,0 +1,13 @@
+package de.darkress.pic16f84sim.commands;
+
+import de.darkress.pic16f84sim.microcontroller.ProgramCounter;
+import de.darkress.pic16f84sim.microcontroller.Stack;
+
+public class Return extends CommandUtils implements Command
+{
+    @Override
+    public void execute()
+    {
+        ProgramCounter.setPcFrom11BitLiteral(Stack.pop());
+    }
+}