add basic command line args

# summary

add command line support to `smfgen`

This is just a proof-of-concept... and is not by any means complete. Let me know what you think about this implementation... it still needs work.

```
$ ./smfgen -i nginx -l 'NGINX Web Server' -s 'nginx -d' -d /var/www -u nobody -g other -p basic -p net_privaddr -eHOME=/var/tmp -ePATH=/bin:/usr/bin
<?xml version="1.0"?>
<!DOCTYPE service_bundle SYSTEM "/usr/share/lib/xml/dtd/service_bundle.dtd.1">
<!-- 
    Manifest automatically generated by smfgen.
 -->
<service_bundle type="manifest" name="application-nginx" >
    <service name="application/nginx" type="service" version="1" >
        <create_default_instance enabled="true" />
        <dependency name="dep0" grouping="require_all" restart_on="error" type="service" >
            <service_fmri value="svc:/milestone/multi-user:default" />
        </dependency>
        <exec_method type="method" name="start" exec="nginx -d &amp;" timeout_seconds="10" >
            <method_context working_directory="/var/www" >
                <method_credential user="nobody" group="other" privileges="basic,net_privaddr" />
                <method_environment >
                    <envvar name="HOME" value="/var/tmp" />
                    <envvar name="PATH" value="/bin:/usr/bin" />
                </method_environment>
            </method_context>
        </exec_method>
        <exec_method type="method" name="stop" exec=":kill" timeout_seconds="30" />
        <template >
            <common_name >
                <loctext xml:lang="C" >NGINX Web Server</loctext>
            </common_name>
        </template>
    </service>
</service_bundle>
```