Add a `#have_put` matcher to test `#put` action.

With this matcher you can test if a content (i.e, a string) is
uploaded to the server. You can also test the path.

Example:

```ruby
it "should have put" do
  @configuration.put 'some: content', '/config.yml'
  @configuration.should have_put('some: content').to('/config.yml')
end
```