Added info_fields option

* Adds additional fields to auth hash as per http://vk.com/dev/fields

* Added info_fields option, a comma-separated list with fields which should
be added to Auth Hash
* Auth Hash contains default fields if option info_fields not specified
Modified info_fields description in README
Merge branch 'feature/info_fields' into develop
Merge branch 'release/0.0.1'
Merge pull request #34 from Sergey-B/master

Add info_fields option