enhanced debugger doc (closes #892)

docs/debugger.html

@@ -349,19 +349,19 @@ size can be configured e.g. in the
     <th>Key</th>
   </tr>
   <tr>
-    <td>Step</td>
+    <td>Step &#185;</td>
     <td>Control + S</td>
   </tr>
   <tr>
-    <td>Trace</td>
+    <td>Trace &#185;</td>
     <td>Control + T</td>
   </tr>
   <tr>
-    <td>Scan +1</td>
+    <td>Scan +1 &#185;</td>
     <td>Control + L</td>
   </tr>
   <tr>
-    <td>Frame +1</td>
+    <td>Frame +1 &#185;</td>
     <td>Control + F</td>
   </tr>
   <tr>
@@ -390,11 +390,12 @@ size can be configured e.g. in the
   </tr>
   <tr>
     <td>Run, exits debugger</td>
-    <td>Backquote (`)</td>
+    <td>Backquote (`), Escape</td>
   </tr>
 </table>
 </p>
 For MacOS use 'Cmd' instead of &nbsp;'Alt' key.
+<p>&#185;: External I/O input is ignored, the state of the <a href="#IOTab">I/O Tab</a> remains unchanged.</p>
 <p>To the left of the global buttons, you find the 'Options...' button.</p>
 <ul>
   <p><img src="graphics/debugger_options.png"></p>