Update docs

[lteacher]

Apparently the docs are really not detailed enough so they could use an update.

Also, if using serveless-offline I needed to expose the reset and use it in the prod handler. I have this code in main handlers.js

const lambda = require('lambda-chain');
const routes = require('./lib/routes');
const { FileEventHandler } = require('./lib/events/file');
const { bodyParser } = require('./lib/utils');

// TODO: Special for serverless-offline, it tries to destroy the node cache
// but the handler factory is a single instance, cached or not.
// Ref: https://goo.gl/54NkoK
lambda.reset();

// Register route handlers
lambda.register(routes);

// Register file event handler
lambda.register({ file: FileEventHandler }, {
  before: bodyParser.parseRequest(),
  after: bodyParser.toJson,
});

module.exports = lambda.exports();

So apparently this link has the problem.

Big thing to document is how the event handler stuff works such as this example node 6 compatible implementation.

const _ = require('lodash');
const { HttpEventHandler } = require('lambda-chain');
const TransformFactory = require('./transform-factory');
const { respond } = require('../../utils');

// Implements the file handler logic for the file http route / event
class FileEventHandler extends HttpEventHandler {
  constructor(event, context) {
    super(event, context);

    this._supportedActions = ['transform'];
  }

  _isSupported(action) {
    return _.includes(this._supportedActions, action);
  }

  _getTransformer(filename, contentType, options) {
    if (filename) return TransformFactory.fromFilename(filename, options);
    if (contentType) return TransformFactory.fromContentType(contentType, options);

    throw new Error('filename or contentType not provided');
  }

  post() {
    const { action, options } = this.event.body;

    return this._isSupported(action) ? this[action](JSON.parse(options || null)) : this.throwUnimplemented(action);
  }

  // Transform some content in the body
  transform(options) {
    // Ensure whatever is coming back is a promise for consistency accross transformations
    return new Promise((resolve) => {
      const { file, filename, contentType } = this.event.body;

      if (!file) throw new Error('No `file` property to transform');

      const transform = this._getTransformer(filename, contentType, options);

      resolve(transform.process(file));
    }).then(result => respond(200, {
      file: {
        data: result,
      },
    }))
    .catch(err => respond(422, { message: err.message }));
  }
}

module.exports = { FileEventHandler };