support for custom insert locations

[iTonyYo]

If you can support custom insert locations, it will be more flexible. In a two-column layout, I want to have it on each side.

Toast.tsx#L37

[iampava]

Hey! You can do this if you insert an element in DOM with id="react-toast". It's not mentioned in README but I found this looking at the code Toast.tsx#L21

[iampava]

On second thought, this will work only if the element is prepended to the DOM before this code runs.

[iampava]

Opened this PR with the feature. Maybe "thumbs up"-it so that the owner can merge it as quickly as possible? #36