indexFunc: compute some basic indexes automatically
In DataShrimp/rating: Rating package based on an index system

These functions are helped to compute some basic indexes automatically, including: Note: the default granularity is month - portion index - yoy index - qoq index - modified yoy index (yoyplus) - modified qoq index (qoqplus) - monthVol index - seasonVol index - yearVol index - monthHhi index - to be added

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1. the index system should have columns: func and parameter
2. prepare the data to specific format: <id, date, value>
3. use getFunction() to load the needed functions and then compute