- added context management support with bopen()
- added bsrch() for Bloomberg SRCH Data
- added parsing to JSON of string representation of Request and Response
messages with parser.py module
- modified ref() to return NaN instead of throwing an error when
fieldException of NOT_APPLICABLE_TO_REF_DATA is given
- modified ref_hist() to support any historical reference date override
instead of just REFERENCE_DATE, e.g. CURVE_DATE