title: logback creates new file every prog restart
body: <p>I have such logback.xmp conf:</p>
  
  <pre><code>&lt;configuration scan="true" scanPeriod="10 seconds" &gt;
  
  &lt;appender name="FILE" class="ch.qos.logback.core.FileAppender"&gt;
      &lt;file&gt;${application.home:-.}/logs/application.log&lt;/file&gt;
      &lt;filter class="ch.qos.logback.classic.filter.ThresholdFilter"&gt;
          &lt;level&gt;DEBUG&lt;/level&gt;
      &lt;/filter&gt;
      &lt;encoder&gt;
          &lt;pattern&gt;[%d{HH:mm:ss}] [%level] - %message%n%xException&lt;/pattern&gt;
      &lt;/encoder&gt;
  &lt;/appender&gt;
  
  &lt;logger name="play" level="WARN"/&gt;
  &lt;logger name="application" level="DEBUG"/&gt;
  
  &lt;logger name="org.jdbcdslog.ConnectionLogger" level="OFF"/&gt; &lt;!-- Won' log connections --&gt;
  &lt;logger name="org.jdbcdslog.StatementLogger" level="INFO"/&gt; &lt;!-- Will log all statements --&gt;
  &lt;logger name="org.jdbcdslog.ResultSetLogger" level="OFF"/&gt; &lt;!-- Won' log result sets --&gt;
  
  &lt;root level="WARN"&gt;
      &lt;appender-ref ref="FILE"/&gt;
  &lt;/root&gt;
  
  &lt;/configuration&gt;
  </code></pre>
  
  <p>Every time I restart my prog it creates new  log file, but in my way I want to continue write logs into old one. So, what is the problem?</p>