documentation for Glow::Role::DirectoryEntry
documentation for Glow::Role::Storage
Glow::Repository::Git requires Digest::SHA
make the classes generated by Glow::Repository::Git immutable
test a simple Storage class

based on the example in Glow::Role::Storage
the content_builder attribute cannot be set in the constructor
required methods for Glow::Role::DirectoryEntry
required methods for Glow::Role::Digest