title: How to align severity to same width in Boost log
body: <p>For example, 'info' and 'warning' have different width, it looks not preety in the log. I want to align them to same width in log.</p>
  
  <p>It seems that I could use customized formatter factory as this article described:
  <a href="https://stackoverflow.com/questions/28359921/boost-log-format-single-attribute-with-logginginit-from-stream">boost log format single attribute with logging::init_from_stream</a></p>
  
  <p>This is another solution by using customized severity level:
  <a href="https://stackoverflow.com/questions/17930553/in-boost-log-how-do-i-format-a-custom-severity-level-using-a-format-string">how do I format a custom severity_level using a format string</a></p>
  
  <p>Besides that, is there an easier way to achieve this by customizing the format string just like printf?</p>