Called by pyang plugin framework at to initialize the plugin.

def pyang_plugin_init():
    """Called by pyang plugin framework at to initialize the plugin."""

    # Register the plugin
    plugin.register_plugin(MDPlugin())

    # Register that we handle extensions from the YANG module
    # 'ietf-yang-metadata'
    grammar.register_extension_module(md_module_name)

    # Register the special grammar
    for (stmt, occurance, (arg, rules), add_to_stmts) in md_stmts:
        grammar.add_stmt((md_module_name, stmt), (arg, rules))
        grammar.add_to_stmts_rules(add_to_stmts,
                                   [((md_module_name, stmt), occurance)])