dsc -- damn small configuration utility.
dsc is very similar to OpenWRT's Unified Configuration Interface.
It keeps configuration values in a hierarchical directory layout.
It has an explicit schema defining what values can be set and how
they must be sanitised.

There are three environmental variables used:
* DSC_SCHEMA -- path to the directory with the schema
* DSC_SAVED -- path to the directory with saved (committed) configuration
* DSC_STASH -- path to the directory with stash (current) uncommitted one

Option's value foo/bar is located in the saved/stash directory in the
"foo" subdirectory, "bar" file.

    $ dsc set foo/bar "my value"
    $ dsc get foo/bar
    my value
    $ dsc get ""
    $ dsc get foo/bar

There are two kind of options: scalar ones, and a dynamic list ones.

    $ dsc add net/iface-name0
    $ dsc add net/iface-name1
    $ dsc get net/*
    iface-name0
    iface-name1
    $ dsc del net/iface-name0
    $ dsc get net/*
    iface-name1
    $ dsc set net/iface-name1/mtu 1300

Schema is a directory with the same hierarchy, but each option is a
directory, that contains:

* "title" file -- with the brief single line description
* optional "descr" file -- with descriptive information
* executable "check" file, that is run when option either is set, or get
  with an empty value. It takes a single argument -- option name. Value
  is read from stdin. If value is not valid, then checker must return
  bad return code, writing the descriptive message to stderr. Otherwise
  the sanitised value is read from stdout. If an input is empty, then
  checker may print default value of the option

Option having "*" name is treated like a dynamic list.

By default all options you set are saved in the stash. "commit" command
will move it to the saved directory. "diff" allows you to see the
difference between the stash and saved directories.