Reject files which is not chkbuild log.
Fix --type option.
Specify an IO object for ChkBuildRubyInfo.new.
Move main() to class method.
Read from stdin only if no filename given as argument.

This commit fixes chkbuild-ruby-info to work with redirect.
Following command didn't work.

% chkbuild-ruby-info < logfile

Following commands didn't work too because chkbuild-ruby-info
reads the output of find command.

% find tmp/public_html/ruby-trunk/log -name '*.log.txt.gz'|sort|
while read fn; do
  echo $fn
  chkbuild-ruby-info $fn > `basename $fn .log.txt.gz`.json
done
Delay output of the first bracket.

This prevents "[" output before "It seems not a chkbuild log.".