ArmaGarch likelihood function
Merge remote-tracking branch 'origin/develop' into develop
new model for likelihood calculations
ARMA + GARCH llh
generalize llh function
update llh calculation
refactor mean & innovations model
fix llh calculation for higher order models
update model
estimation & forecasting
remove old model & update readme
Merge pull request #2 from ezhulenev/develop

support for ARMA mean model