Fixed missing enum extend. #137

[dcaoyuan]

Added enum extend.

[alaa-eddine]

Merged, please note that I will change it to this, in order to match Pine Script internal representation

export enum extend {
    left = 'l',
    right = 'r',
    both = 'b',
    none = 'n',
}

there are also some other impacted types like belowbar, abovebar becoming BelowBar, AboveBar
and arrowup, arrowdown becoming shape_arrow_up, shape_arrow_down ...etc

I changed many Type enums values to match internal tradingview representation

In tradingview you can get the actual representations by using a code like this :

log.info('{0} {1} {2} {3} {4} {5}', str.tostring(location.abovebar), str.tostring(location.belowbar), str.tostring(location.top), str.tostring(location.bottom), str.tostring(location.absolute))