Split off digest utils module
Revert "Drop digest class configuration"

This reverts commit 0e07806b14a92abc6b205b27e15375dfe40b5e4d.
Reduce hard coded SHA256 digest copy
Mix digest utils into env
Defer to env digest class
Improve reverse lookup of digest class
Merge branch 'master' into 4.x

Conflicts:
	lib/sprockets/utils.rb