New file price_transform.go implements five new public wrappers:
- AvgPrice (TA_AVGPRICE) – mean of OHLC per bar
- MedPrice (TA_MEDPRICE) – (High + Low) / 2
- TypPrice (TA_TYPPRICE) – (High + Low + Close) / 3
- WCLPrice (TA_WCLPRICE) – (High + Low + 2×Close) / 4
- AvgDev (TA_AVGDEV) – rolling average absolute deviation from SMA
- add corresponding low-level function pointer signatures in functions.go
- register all five symbols in Load() in loader.go
- update README.md with Price Transforms and Statistic Functions sections
