Provides a method that will give an upper bound on the size of a rangeproof,
given an upper bound on the value to be passed in and an upper bound on the
min_bits parameter.
There is a lot of design freedom here since the actual size of the rangeproof
depends on every parameter passed to rangeproof_sign, including the value to
be proven, often in quite intricate ways. For the sake of simplicity we assume
a nonzero `min_value` and that `exp` will be 0 (the default, and size-maximizing,
choice), and provide an exact value for a proof of the given value and min_bits.
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