Added to_yaml & from_yaml (as well as to_hash & from_hash)

[srushti]

Mail::Message#to_yaml used to give an error earlier.
TypeError: can't dump anonymous class Class

[mikel]

Awesome, thanks for your work, however, the specs fail on the latest master. There was an error in the spec regexp which I fixed.

[mikel]

I have merged this in.

[sandstrom]

Is this [pull request] compatible with YAML::dump? Unless I'm missing something it seems not.

>> m1 = Mail::Message.new
=> #<Mail::Message:2190471100, Multipart: false, Headers: >
>> YAML::dump m1
ArgumentError: wrong number of arguments (1 for 0)
    from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/yaml.rb:117:in `to_yaml'
    from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/yaml.rb:117:in `dump'
    from (irb):15
>> YAML::VERSION
=> "0.60"
>> Mail::VERSION.version
=> "2.2.19"
>> 

Also, the current serialization isn't a full representation of the Message object. Many instance variables aren't included, e.g. delivery_handler.

[sandstrom]

This is the implementation used in Object:

  YAML::quick_emit( self, opts ) do |out|
    out.map( taguri, to_yaml_style ) do |map|
      to_yaml_properties.each do |m|
        map.add( m[1..-1], instance_variable_get( m ) )
      end
    end
  end

[urbanautomaton]

To address some of the issues raised by sandstrom (as I ran into precisely the same problem with the missing fields), I've made a couple of changes and submitted pull request #237 - details can be found there.

(I haven't addressed the YAML::dump issue though) Edit: now I have.