This is an example of a package declaration. The declaration
begins with the keyword PACKAGE and the name of the package followed
by the keyword IS. VHDL declaration statements are then included,
such as type declarations, constant declarations, and
subprogram declarations. The package declaration lists
the contents of the package. For many VHDL constructs, such as types,
declarations are sufficient to fully define them. For a subprogram,
however, the declaration only specifies the parameters required by the
function or procedure; the operation of the subprogram appears later
in the package body. The package declaration ends with
END and the package name.
