-v prints version and do something

Without this patch, `rdbg -v target.rb` prints version and terminates
the process. With this pach, `-v` prints version and starts debugging
for `target.rb`.

If no filename is given, terminates the process.

Author: ko1

lib/debug/config.rb

@@ -265,6 +265,8 @@ def self.parse_argv argv
       require 'optparse'
       require_relative 'version'
 
+      have_shown_version = false
+
       opt = OptionParser.new do |o|
         o.banner = "#{$0} [options] -- [debuggee options]"
         o.separator ''
@@ -372,6 +374,16 @@ def self.parse_argv argv
         o.separator ''
         o.separator 'Other options:'
 
+        o.on('-v', 'Show version number') do
+          puts o.ver
+          have_shown_version = true
+        end
+
+        o.on('--version', 'Show version number and exit') do
+          puts o.ver
+          exit
+        end
+
         o.on("-h", "--help", "Print help") do
           puts o
           exit
@@ -395,6 +407,14 @@ def self.parse_argv argv
 
       opt.parse!(argv)
 
+      if argv.empty?
+        case
+        when have_shown_version && config[:mode] == :start
+          pp config
+          exit
+        end
+      end
+
       config
     end