Interface for url provider

[NathanCheshire]

Define some interface which the get url method should accept. Our own builder can implement this interface and this will also allow others to define their own if for some reason they want hooks or more functionality.

[NathanCheshire]

/**
* An interface for classes to implement which provide an API for Gravatar image requests.
*/
public interface GravatarImageRequestBuilder {
   /**
     * Sets whether the JPG suffix should be appended to the user email hash when constructing the image request url.
     *
     * @param appendJpgSuffix whether the JPG suffix should be appended to the
     *                       user email hash when constructing the image request url.
     * @return this builder
     */
    public GravatarImageRequestBuilder setAppendJpgSuffix(boolean appendJpgSuffix);

     /**
     * Sets the size for the image to be returned by this image request.
     *
     * @param size the requested size
     * @return this builder
     */
    public GravatarImageRequestBuilder setSize(int size);

    /**
     * Sets the ratings to the provided collection of ratings.
     *
     * @param ratings the collection of ratings
     * @return this builder
     */
    public GravatarImageRequestBuilder setRatings(Collection<GravatarRating> ratings);

  /**
     * Sets the ratings to the provided singular rating.
     *
     * @param rating the rating
     * @return this builder
     */
    public GravatarImageRequestBuilder setRating(GravatarRating rating);

   /**
     * Adds the ratings to the provided collection of ratings.
     *
     * @param ratings the collection of ratings to add
     * @return this builder
     */
    public GravatarImageRequestBuilder addRatings(Collection<GravatarRating> ratings);

  /**
     * Adds the rating to the list of ratings.
     *
     * @param rating the rating to add
     * @return this builder
     */
    public GravatarImageRequestBuilder addRating(GravatarRating rating);

 /**
     * Sets whether to force the default image to be returned from this image request,
     * regardless of whether the a Gravatar for the user email is valid.
     *
     * @param forceDefaultImage whether to force the default image to be returned
     * @return this builder
     */
    public GravatarImageRequestBuilder setForceDefaultImage(boolean forceDefaultImage);

    /**
     * Sets the default image type to the provided type.
     * Note, this removes the value set by {@link #setDefaultImageUrl()} if set.
     *
     * @param defaultImageType the default image type
     * @return this builder
     */
    public GravatarImageRequestBuilder setDefaultImageType(GravatarDefaultImageType defaultImageType);

    /**
     * Sets the default image url.
     * Note, this removes the value set by {@link #setDefaultImageType()} if set.
     *
     * @param defaultImageUrl the default image url
     * @return this builder
     */
    public GravatarImageRequestBuilder setDefaultImageUrl(String defaultImageUrl);

    /**
     * Builds the Gravatar image request url represented by the current state of this builder.
     *
     * @return the Gravatar image request url
     */
    public String buildUrl();
}