add t-dist table and getProbability
add dickey-fuller test
add lag and diff method and depends on js-object-clone
Merge branch 'feature/diff' into feature/unitroottest
add t-distribution and diff, lag
add yule-walker resolution and ar model
Merge branch 'feature/unitroottest'
Merge branch 'feature/arima'
Bump version 0.0.2