Adds custom_methods to RestUp via options

@RasterBurn this is simple implementation allows custom methods to be added to resource apis. Here's a simple example:
```
var model = require('model'),
    api = restUp({
		custom_methods: ['search']
	})
	.resource('users')
		.get(model.getUser)
		.post(model.addUser)
		.put(model.updateUser)
		.delete(model.deleteUser)
		.search(model.searchUser)
	.end();

var myQuery = {...};
api().users().search(myQuery);
```