Linear Regression (linreg)

``` use linregrs::LinReg; use tacommon::traits::Indicator;

let mut linreg = LinReg::new(5); asserteq!(linreg.next(81.59), None); asserteq!(linreg.next(81.06), None); asserteq!(linreg.next(82.87), None); asserteq!(linreg.next(83.00), None); asserteq!(linreg.next(83.61), Some(83.622)); asserteq!(linreg.next(83.15), Some(83.72199999999998)); asserteq!(linreg.next(82.84), Some(83.11199999999998)); asserteq!(linreg.next(83.99), Some(83.55999999999997)); asserteq!(linreg.next(84.55), Some(84.17199999999997)); asserteq!(linreg.next(84.36), Some(84.60399999999998)); asserteq!(linreg.next(85.53), Some(85.40399999999998)); asserteq!(linreg.next(86.54), Some(86.20999999999998)); asserteq!(linreg.next(86.89), Some(86.94599999999997)); asserteq!(linreg.next(87.77), Some(87.85399999999996)); assert_eq!(linreg.next(87.29), Some(87.75399999999996));

```