Split digest/hexdigest/base64digest
Switch to SHA256
Compute raw digest bytes instead of hex
Use raw digest for dependency source paths
Store raw byte digest on asset
Generate integrity from existing digest
Prefer hexdigest when possible
Note Asset#digest change
Correct default digest changelog
Build integrity before asset id
Deprecate digest_class in docs
Merge pull request #647 from sstephenson/digest-redux

SHA256 everywhere