implemented Clrw instruction (#15)

Co-authored-by: darkress <github@darkress.xyz>
Reviewed-on: darkress/pic16f84-sim#15

de/darkress/pic16f84sim/commands/Clrw.java

@@ -0,0 +1,18 @@
+package de.darkress.pic16f84sim.commands;
+
+import de.darkress.pic16f84sim.microcontroller.Memory;
+import de.darkress.pic16f84sim.microcontroller.ProgramCounter;
+
+public class Clrw extends FileRegisterCommandUtils implements Command
+{
+    @Override
+    public void execute()
+    {
+        final int result = 0;
+
+        checkZeroBit(result);
+
+        Memory.workingRegister = result;
+        ProgramCounter.incPC();
+    }
+}