"standby promote": make timeout values configurable

This introduces following new configuration file parameters, which
were previously hard-coded values:

 - promote_check_timeout
 - promote_check_interval

Implements GitHub #387.

doc/repmgr-standby-promote.sgml

@@ -26,6 +26,12 @@
       by using <xref linkend="repmgr-standby-follow">; if <application>repmgrd</application>
         is active, it will handle this automatically.
     </para>
+    <para>
+      Note that &repmgr; will wait for up to <varname>promote_check_timeout</varname> seconds
+      (default: 60 seconds) to verify that the standby has been promoted, and will
+      check the promotion every <varname>promote_check_interval</varname> seconds (default: 1 second)
+      (both values can be defined in <filename>repmgr.conf</filename>).
+    </para>
   </refsect1>
 
   <refsect1>
@@ -42,6 +48,7 @@
     </para>
   </refsect1>
 
+
   <refsect1>
     <title>Event notifications</title>
     <para>

doc/repmgr-standby-unregister.sgml

@@ -43,6 +43,22 @@
     </para>
   </refsect1>
 
+  <refsect1>
+    <title>Options</title>
+    <variablelist>
+
+      <varlistentry>
+        <term><option>--node-id</option></term>
+        <listitem>
+          <para>
+            <varname>node_id</varname> of the node to unregister (optional)
+          </para>
+        </listitem>
+      </varlistentry>
+
+    </variablelist>
+  </refsect1>
+
   <refsect1>
     <title>Event notifications</title>
     <para>