feat: allow custom models

[rawkode]

Example Blox:

base: tests
source: data
destination: out
templates: templates
default_extension: .md
models:
  # - id: profile
  #   name: Profile
  #   cue: |
  #     {
  #       name: string
  #     }
  - id: tweet
    name: Tweet
    folder: tweet
    foreignkey: tweet_id
    cue: |
      {
        tweet: "two"
      }