fix imports
added docstring and move comment to proper format
updated imports and some fixes
allow creating Euribor6M without term structure
support more variations of the SwapRateHelper constructor
WIP: more fixes to the swap example
fix read_csv call and filtering good rows
fixes to imports and processing (changes in pandas api)
fix heston_calibration.py script and OptionQuotes target file
update to data files
latest changes to have the demo working
Added implied volatility to DividendVanillaOption class