- add native TA-Lib bindings in functions.go for beta, correl, linear regression, stddev, tsf, and variance
- register the new TA-Lib symbols in loader.go
- add public wrappers in statistic_functions.go for Beta, Correl, LinearReg, LinearRegAngle, LinearRegIntercept, LinearRegSlope, StdDev, TSF, and Var
- update README.md to document Price Transforms and Statistic Functions
