Added adapter base class and made all adapters inherit from it
Added load_options/dump_options to MultiJson
Added load_options/dump_options to adapters as well
Using load_options/dump_options for passing options to adapter instance

Deprecated MultiJson.default_options
Cleaned Oj and JsonCommon adapter using new Adapter.defaults API
Merge pull request #91 from intridea/default-options

Default options