Various CreditMemo related items:
1. :placed_on should be depreciated on the next major release. Replace
it with :txn_date as it is the standard across the models.
2. :place_on should be :as => Date
3. Dry up ensure_line_items_initialization by putting it in
BaseModel. Add ensure_line_items_initialization to CreditMemo.
It is .now not .new and use a more lenient regex.
Travis does not like + sign in utc.
Readme update. The documentation specifically says that OR operations are not supported

Relevant url: https://developer.intuit.com/docs/0025_quickbooksapi/0050_data_services/020_key_concepts/00300_query_operations/0500_simplified_syntax

"The WhereClause filters the returned data according to the value of a property.

Note: Multiple clauses (filters) are AND'd.  The OR operation is not supported."
Merge pull request #95 from markrickert/readme-or-and

Readme update. The documentation specifically says that OR operations are not supported
Merge pull request #94 from minimul/credit-memo-items

Various CreditMemo related items: