Added docs and added new context based plugins.

PLUGINS.md

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+# Talk Plugins
+
+Plugins for Talk can take various forms, currently we are only supporting server
+side plugins.
+
+## Plugin Registration: `plugins.json`
+
+All plugins must be registered in the root file `plugins.json`.
+
+The format for this file is thus:
+
+```js
+{
+  "server": [
+    "people"
+  ]
+}
+```
+
+Where we have a `server` key with an array of plugins that match the folder
+name in the `plugins/` folder. For example, the above `plugins.json` would
+require a plugin from `plugins/people`, which must provide a `index.js` file
+that returns an object that matches the Plugin Specification.
+
+## Server Plugins
+
+### Specification
+
+Each plugin should export a single object with all hooks available on it.
+
+_**Note: You will have access to the whole core and other plugin's typeDefs,
+context, loaders, mutators, resolvers, hooks. This is intentional, as it
+encourages composing plugins to merge functionality, like a Slack plugin which
+provides a Slack notify context function as well as having the loader for
+comments.**_
+
+The following are the hooks available:
+
+#### Field: `typeDefs`
+
+```graphql
+enum COLOUR {
+  RED
+  BLUE
+}
+
+type Person {
+  name: String!
+  colour: COLOUR!
+}
+
+type RootMutation {
+  createPerson(name: String!): Person
+}
+
+type RootQuery {
+  people: [Person!]
+}
+```
+
+Thanks to [gql-merge](https://www.npmjs.com/package/gql-merge) the contents of
+`typeDefs` should be a string that will be _merged_ with the existing type
+definitions. `enum`'s will be appended to, types will be appended, and new types
+will be added.
+
+#### Field: `context`
+
+```js
+{
+  Slack: (context) => ({
+    notify: (message) => {
+      // return a promise after we're done sending notifications.
+    }
+  })
+}
+```
+
+Any property provided here will be added to the context parameter available
+inside all resolvers, loaders, mutators, and of course, other context based
+plugins.
+
+The top level item must accept a context for the request which it should use to
+configure the context plugin before it would be mounted at `context.plugins`.
+This plugin above would mount at: `context.plugins.Slack`, or, if you're using
+[object destructuring](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment), `{plugins: {Slack}}`.
+
+#### Field: `loaders`
+
+```js
+(context) => ({
+  People: {
+    load: () => db.people.find({user: context.user})
+  }
+})
+```
+
+Loaders should be provided as a function which returns a map which is used in
+the resolvers function. These must return a promise or a value.
+
+#### Field: `mutators`
+
+```js
+(context) => ({
+  People: {
+    create: (name) => {
+      return db.people.insert({user: context.user, name});
+    }
+  }
+})
+```
+
+Mutators should be provided as a function which returns a map which is used in
+the resolvers function. These must return a promise or a value.
+
+#### Field: `resolvers`
+
+```js
+{
+  Person: {
+    name(obj, args, context) {
+      return obj.name;
+    },
+    colour(obj, args, context) {
+      // Bill likes the colour red, everyone else likes blue.
+      return obj.name === 'bill' ? 'RED' : 'BLUE';
+    }
+  },
+  RootQuery: {
+    people(obj, args, {loaders: {People}}) {
+      return People.load();
+    }
+  },
+  RootMutation: {
+    createPerson(obj, {name}, {mutators: {People}}) {
+      return People.create(name);
+    }
+  }
+}
+```
+
+Should return a resolver map as described in the
+[Apollo Docs](http://dev.apollodata.com/tools/graphql-tools/resolvers.html#Resolver-map).
+
+This will merge with the existing resolvers in core and from previous plugins.
+
+#### Field: `hooks`
+
+```js
+{
+  RootMutation: {
+    createPerson: {
+      post(obj, args, {plugins: {Slack}}, person) {
+        if (!person) {
+          return person;
+        }
+
+        await Slack.notify(`A new person just was created with name ${person.name}`);
+
+        return person;
+      }
+    }
+  }
+}
+```
+
+Hooks here are pretty special, for each resolver field, you can specify a
+pre/post hook that will execute pre and post field resolution.
+
+If your post function accepts four parameters, then it can modify the field
+result. It is *required* that the function resolves a promise (or returns) with
+the modified value or simply the original if you didn't modify it.
+
+### Full Example
+
+Contents of `plugins.json`:
+
+```json
+{
+  "server": [
+    "people"
+  ]
+}
+```
+
+Located in `plugins/people/index.js`:
+
+```js
+module.exports = {
+  typeDefs: `
+  enum COLOUR {
+    RED
+    BLUE
+  }
+
+  type Person {
+    name: String!
+    colour: COLOUR!
+  }
+
+  type RootQuery {
+    people: [Person!]
+  }
+  `,
+  context: {
+    Slack: () => ({
+      notify: (message) => {
+        // return a promise after we're done sending notifications.
+      }
+    })
+  },
+  loaders: ({user}) => ({
+    People: {
+      load: () => db.people.find({user})
+    }
+  }),
+  mutators: ({user}) => ({
+    People: {
+      create: (name) => {
+        return db.people.insert({user, name});
+      }
+    }
+  }),
+  resolvers: {
+    Person: {
+      name(obj, args, context) {
+        return obj.name;
+      },
+      colour(obj, args, context) {
+        // Bill likes the colour red, everyone else likes blue.
+        return obj.name === 'bill' ? 'RED' : 'BLUE';
+      }
+    },
+    RootQuery: {
+      people(obj, args, {loaders: {People}}) {
+        return People.load();
+      }
+    },
+    RootMutation: {
+      createPerson(obj, {name}, {mutators: {People}}) {
+        return People.create(name);
+      }
+    }
+  },
+  hooks: {
+    RootMutation: {
+      createPerson: {
+        post(obj, args, {plugins: {Slack}}, person) {
+          if (!person) {
+            return person;
+          }
+
+          await Slack.notify(`A new person just was created with name ${person.name}`);
+
+          return person;
+        }
+      }
+    }
+  }
+};
+
+```