Support <worker N-M> syntax

[repeatedly]

This feature improves multi process usage.
Currently, <worker> section takes only 1 number and it can't define multiple input plugins to share port.
<worker N-M> resolves the problem like below.

<worker 0-4>
  <source>
    @type tcp
  </source>
  <match pattern>
    # ...
  </match>
</worker>

<worker 5-10>
  <source>
    @type forward
  </source>
  <match pattern>
    # ...
  </match>
</worker>

This patten is popular in large scale deployment so adding this syntax helps users.