Refactored BaseTransaction to add Account

Refactored BaseTransaction into BaseService and now Transaction and Account extends of it.
Refactored ResponseParsers

Added TransactionResponseParser and AccountResponseParser extending from ResponseParser to more easily manage each response.
Refactored ParamParsers

Refactored ParamParsers to adapt to the new response parsers.
Added account documentation in README
Fixed README's identation
Merge pull request #3 from efreesen/master

Account