Clopper Pearson Confidence level

The error for efficiency was derived from the Poisson error, which is unsuitable for efficiency. Change to Clopper Pearson confidence level, which is conservative when the number of trials is low (e.g 10) but equal to binomial when the number of trials is high (e.g., 5000). It gives "better" error estimation when the efficiency is very close to one. Better means it gives non-zero values.

The attached plot compares four different error estimations.