Capitalize error messages from yaml_fs storage backend

Signed-off-by: martin f. krafft <madduck@madduck.net>
Add verbosity/debugging output to TODO

Signed-off-by: martin f. krafft <madduck@madduck.net>
Make exiting with message a function of the exception

Signed-off-by: martin f. krafft <madduck@madduck.net>
Add an exception for permission errors

Signed-off-by: martin f. krafft <madduck@madduck.net>
Add deprecation notice to Ansible adapter module

Signed-off-by: martin f. krafft <madduck@madduck.net>
Update docs to reflect ext_pillar taking a list

Signed-off-by: martin f. krafft <madduck@madduck.net>
Massive refactoring

This commit does some massive refactoring of the Salt source:

  - reclass and all adapters have been changed to support the distribute
    (setuptools) entry-points interface, while they are also runnable
    directly (using `/usr/bin/env python`);

  - reclass and all adapters now use exactly the same approach to
    configuration (sensible defaults + config file + command-line
    options), but inventory/nodeinfo is properly parametrised (e.g.
    top/pillar for Salt);

  - the documentation has been updated accordingly;

  - defaults and constants were factored out into common modules.

Signed-off-by: martin f. krafft <madduck@madduck.net>