This funcion is called internally by applyStrategy in normal
operation, but it is also useful for nanual testing during development.
If you are using this function to test your strategy, note that the 'mktdata'
argument should likely contain the output of applyIndicators.
applySignals(strategy, mktdata, indicators = NULL, parameters = NULL,
...)an object of type 'strategy' to add the signal to
an xts object containing market data. depending on signals, may need to be in OHLCV or BBO formats
if indicator output is not contained in the mktdata object, it may be passed separately as an xts object or a list.
named list of parameters to be applied during evaluation of the strategy
any other passthru parameters