PromiseResult type

[gagdiez]

In #82 the PromiseResult type was changed to string | near.PromiseResult.NotReady | nearPromiseResult.Failed.

From the method's signature it looks like checking for errors would be:

if(near.promiseResult() == near.PromiseResult.Failed){ near.log("the xcc failed") }

However, if a method return the value of 2 it will be falsely assumed there was an error (I tested it in this transaction).

In an scenario such as handling FT, where methods return how many tokens were used, this could lead to potentially devastating errors.

The previous return{status, value} was clear, for which I vote for rolling it back.