[feature] Add optimistic update on create

[ntucker]

Fixes #96

Motivation

Provide both the mechanism for common case optimistic updates, as well as well designed extension points for unusual cases like #124

Solution

Update the API of the function returned from useFetcher to take in an array of updaters:

const createArticle = useFetcher(ArticleResource.createShape());

createArticle({ id: 1 }, {}, [
  [ArticleResource.listShape(), {}, (newArticle, articles) => [...articles, newArticle]]
])

Additionally, this supports the same case for GETs, in the case of pagination:

class PaginatedArticleResource extends Resource {
  readonly id: number | null = null;
  readonly title: string = '';
  readonly content: string = '';
  readonly author: number | null = null;
  readonly tags: string[] = [];

  pk() {
    return this.id;
  }

  static urlRoot = 'http://test.com/article/';

  static listShape<T extends typeof Resource>(this: T) {
    return {
      ...super.listShape(),
      schema: { results: [this.getEntitySchema()] },
    };
  }
}

function mergeArticles(
  newPage: { results: string[] },
  articles: { results?: string[] },
): { results: string[] } {
  return [...(articles.results || []), ...newPage.results];
}

function useNextPageFetcher() {
  const getNextPage = useFetcher(ArticleResource.listShape());
  return useCallback(() => {
    return getNextPage({}, { cursor: 2 }, [
      [ArticleResource.listShape(), {}, mergeArticles],
    ]);
  }, [getNextPage]);
}

Credit

@zacharyfmarion wrote much of this code, but was rebased together so this attribution was lost in this PR