Completed the attribute support for servers. (#95)

* Completed the attribute support for servers, and password is optional. Resolves #92.

* Updated oracleServers.xml template to match new servers.xml template.

* Revised tests to match code and template changes.

* Added documentation for server attributes.

* Added additional use cases to exercise server attribute handling.

README.md

@@ -40,6 +40,18 @@ steps:
     servers: '[{"id": "serverId", "username": "username", "password": "password"}]'
 ```
 
+All `server` attributes may be specified:
+  * `id` _(required)_
+  * `username`
+  * `password`
+  * `privateKey`
+  * `passphrase`
+  * `filePermissions`
+  * `directoryPermissions`
+  * `configuration`
+
+Please refer to the [servers](http://maven.apache.org/settings.html#Servers) documentation for more information.
+
 ## ```settings.xml``` with servers section and additional configuration
 
 ``` yml