Added rewarded ad size

[britzl]

CHANGE: The poki_sdk.rewarded_break() function now expects an ad size string ("small", "medium", "large") as first argument:

local size = "small"
poki_sdk.rewarded_break(size, callback)

[erikdubbelboer]

@britzl is it possible to make this param optional?

[AGulev]

+1 to @erikdubbelboer
that would be nice to make it "small" by default if the first parameter is a function

[AGulev]

👍