An enumeration of known valid military and civilian/idustrial agencies.
An Agency is the highest-level meaningful organization description
associated with a lower-level organization.
Military Agencies are generally the CINC-level descriptions of
affiliation. E.g. Usually "USTC" rather than "TCJ6".
The implementation attempts to keep the number of duplicate Agency
instances (e.g. that are .equals) to a minimum, but there are situations
where this is not practical. Use .equals instead of ==.
Constructor takes a String that represents the named Agency.
It is preferred to use the constant Agencies or the getAgency
method rather than to use the constructor.