The module directory class supports both the export and
export_source targets, just like the top level. This enables
individual modules to be released as separate entities.
The mandatory tokens supported by the module class are VERSION
and DESCRIPTION. The values of these tokens are used to
provide information for the selection of modules at user ASTERIX startup.
A module must supply a startup script for each supported shell (currently
only csh). This script is sourced for each module that is
to be initialised.
The module class obeys the EXPORT and EXPORT_SOURCE targets
which construct binary+source and source only module releases respectively. The
module release is written to a compressed tar file, the location of which
is specified using the EXPORT environment variable, the default
being the current directory, ie. the module top level directory. This
facility can be used to release modules of ASTERIX separately of other
modules.