This introduces more accurate timing formulas associated with the "Hidden" mod (previously, in #115, these values were hardcoded). The values seem somewhat close to the values in osu!, but were not extensively tested.
Also set an upper bound on the fade in time for hit objects proportional to the approach time, or else the timing values in the "Hidden" mod would be too inconsistent.
Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>
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