implement support for multiple verb-ed instance methods

Adds support for changing, setting user passwords

```
user = ZendeskAPI::User.new(client, :id => 1)
user.set_password!(:password => "hello") # POST /api/v2/users/:id/password
user.change_password!(:old_password => "hello", :new_password => "test") # PUT /api/v2/users/:id/password
```

Issue #119
add support for Ticket#mark_as_spam

```
ticket = ZendeskAPI::Ticket.new(client, :id => 123)
ticket.mark_as_spam! # PUT /api/v2/tickets/:id/mark_as_spam
```

issue #132