Configure modulecmd with config sub-command

The config sub-command has been added to module to help getting or setting the modulecmd.tcl options. With no additional command-line argument, this sub-command reports the current value of all existing options with a mention to indicate if this value has been overridden from a command-line switch or from an environment variable.

See the description of this sub-command in the module man page for a complete reference on existing configuration options.

Most of the options can be altered by passing the option name and a value to the sub-command. Setting an option by this mean overrides its default value, set at installation time in modulecmd.tcl script, by defining the environment variable which supersedes this default.:

$ module config auto_handling 1
$ module config auto_handling
Modules Release 4.3.0 (2019-XX-XX)

- Config. name ----.- Value (set by if default overridden) ----------
auto_handling 1 (env-var)

When command-line switch --reset and an option name is passed to the config sub-command, it restores default value for configuration option by unsetting related environment variable.

With command-line switch --dump-state, the config sub-command reports, in addition to currently set options, the current state of modulecmd.tcl script and Modules-related environment variables. Providing the output of the module config --dump-state command when submitting an issue to the Modules project will help to analyze the situation.

This change is available in git repository and will be included into the next feature release v4.3.