Continue design changes to address issues #57, #39, #48

A directory listed under the "paths" field of a parent metadata delegation is understood to mean all
subdirectories and files the delegated role is trusted to update.  The delegated role has the option
of specifying multiple, arbitrary, and explicit file paths & directories.  The previous implementation
allowed explicit file paths in the "paths" field of the parent role metadata.  This commit modified
this behaviour to allow directories (replicating wildcards) to minimize the size of parent metadata.