Feature Gate Various Instructions

[bonedaddy]

Overview

Not everyone many need all the sighashes offered. Using cargo features we can selectively enable various instructions, preserving program space.

The only "scalable" categorization system I can think of is grouping instructions by the first letter of the instruction name. This way you can include all instructions that start with the letter d using:

sighashdb = {version = "0.1.5, features = ["d"]}