[feature request] Backport smart fees from bitcoin core #1669
Description
Bitcoin core has a better fee algorithm in 0.15.0
See bitcoin#10199 and other commits in the directory
It returns more accurate fees and returns fees even for small / big block targets. (With very empty chains, current algoritm returns -1 for small targets, and for targets >= 25)
The more accurate fees are maybe not important for emptier blockchains like Dash, but the API is already better, because it doesn't return -1 for either too small targets or too big targets.