How to add new features

Steps required to add new features to the code:

1) add the new feature name to the featureNames array below 2) add a uint256 declaration for the feature to the bottom of this file 3) add a uint256 definition for the feature to the corresponding source file (Feature.cpp) 4) if the feature is going to be supported in the near future, add its sha512half value and name (matching exactly the featureName here) to the supportedAmendments in Feature.cpp.