static async fromLUAsync(luArray, luSearchFn) {
        if(!Array.isArray(luArray)){
            if (luArray instanceof LU)
                luArray = new Array(luArray)
            else 
                luArray = new Array(new LU(luArray))
        }
        let parsedContent = await build(luArray, false, '', luSearchFn)
        parsedContent.validate()
        return parsedContent
    }
Builds a Luis instance from a Lu list.
@param {Array<LU>} luArray Array of LU files to be merge
@param {function} luSearchFn function to retrieve the lu files found in the references
@returns {Luis} new Luis instance
@throws {exception} Throws on errors. exception object includes errCode and text.