- add TA-Lib function pointer signatures for ATR/NATR/TRANGE and AD/ADOSC/CMF/NVI/OBV/PVI/PVO in functions.go
- register new native symbols in loader.go
- add new wrapper sources: volatility_indicators.go and volume_indicators.go
- update README function matrix with new volatility and volume categories
- add ta-lib upstream as a git submodule (.gitmodules + ta-lib gitlink)
