Added Money#to_json method

[rwz]

No description provided.

[weppos]

Do we really need a to_json, to_xml, to_yaml, ... feature?

I'm not really sure they makes sense because users might want to use a different to_json logic depending on your application.

Also, it is worth to mention that, by default, the JSON library adds a to_json method at Object level. It means, every object is "jsonificable". The way it works by default, is to export all the internal object attributes.
Last but not least, a Money#to_json might probably require a Money.from_json counterpart.

From my very personal point of view, I would delegate the responsibility to create a to_json method to the final user.

[weppos]

Also, it's important to keep in mind that the JSON library is actually a gem and is not part of the Ruby Standard Library, at least in Ruby 1.8.7. What if I want to use Yajl instead of JSON? Or any other library? I would have to re-implement this method in any case.

[rwz]

Well, i saw JSON.dump in other parts of the code, for example in VariableExchange#export_rates. so i concluded it's safe to use it . Anyway, it can be easy implemented with only string interpolation.

I only implemented it because Object#to_json is way too verbose for Money object. It looks something like:

{"cents"=>1000,
 "currency"=>
  {"id"=>"usd",
   "priority"=>1,
   "iso_code"=>"USD",
   "name"=>"United States Dollar",
   "symbol"=>"$",
   "subunit"=>"Cent",
   "subunit_to_unit"=>100,
   "symbol_first"=>true,
   "html_entity"=>"$",
   "decimal_mark"=>".",
   "thousands_separator"=>","},
 "bank"=>{"rounding_method"=>nil, "rates"=>{}, "mutex"=>{}}}

[semmons99]

I'm going to leave this to users to define. The only reason that banks have #to_json methods is to easily unload and load rates.