removing prettyprint from swap conventions
new currency_registry, moved all the currency related modules under
quantlib/currency/
removed term_structure_factory function (should be using the
PiecewiseYieldCurve constructor)
fixing tests to use the new currency_registry and no more
term_structure_factory
removed help method from Currency (should use docstring or the registry)
refactored help methods of Thirty360 and ActualActual in favour of using a
docstring
removed prettyprint module, replaced by tabulate
expose BusinessDayConvention in quantlib.time.api, refactor its help method in
a docstring
remove unused DataStore
cleanup of imports
fix broken generated docstring
cleanup of the IMM functions
updated docstring
delay import