Initial pass at implementing journal entries.
Adds Entity model and journal entry line detail.
Merge branch 'master' of https://github.com/ruckus/quickbooks-ruby into journal-entry

# By Cody Caughlan (4) and others
# Via Cody Caughlan (4) and bhaity (1)
* 'master' of https://github.com/ruckus/quickbooks-ruby:
  include sales receipt instructions in readme
  Added section to README about persisting the access credentials
  Add AutoDocNumber support to SalesReceipt. Closes #105
  ensure line items initialization when creating new sales receipt
  version bump
  formatting cleanup
  Search_name_query shouldn't be private.
  Make sure all service model classes are marked as private.
  Move default_model_query to BaseService class.
  Make all BigDecimal :to_xml use the to_xml_big_decimal helper method.
Indicate that journal entries are implemented in the readme.
Merge pull request #112 from markrickert/journal-entry

JournalEntry implemented