Add Async Idempotent Writes presentation

Add link in README and opening and closing slides.
Add `beige` npm script

Run reveal server with the `beige` theme.
Idempotent Writes: Add opening overview of talk
Idempotent Writes: Add Lola overview
Idempotent Writes: Rephrase opening

Mention that the project is an API and that we will talk about the patterns I used.
Idempotent Writes: Add questions slide
Idempotent Writes: Add problems section

Text diagrams, baby!
Idempotent Writes: Add asynchronous section
Idempotent Writes: Add idempotent section
Idempotent Writes: Add `$set` pattern section
Idempotent Writes: Add `$set` problem discussion
Idempotent Writes: Add `processed` pattern section
Idempotent Writes: Add `upsert` section
Merge branch 'idempotent-writes'

* idempotent-writes:
  Idempotent Writes: Add `upsert` section
  Idempotent Writes: Add `processed` pattern section
  Idempotent Writes: Add `$set` problem discussion
  Idempotent Writes: Add `$set` pattern section
  Idempotent Writes: Add idempotent section
  Idempotent Writes: Add asynchronous section
  Idempotent Writes: Add problems section
  Idempotent Writes: Add questions slide
  Idempotent Writes: Rephrase opening
  Idempotent Writes: Add Lola overview
  Idempotent Writes: Add opening overview of talk
  Add `beige` npm script
  Add Async Idempotent Writes presentation