Consider allowing anonymous function expressions

At the moment [you forbid](https://github.com/airbnb/javascript/blob/ea093e0373cc4dfa07c69ef7c75d81bd06bdf0c2/packages/eslint-config-airbnb/.eslintrc#L140) unnamed function expressions like `function() {}`. That’s a good thing.

But when using the new function bind syntax with **[trine](https://github.com/jussi-kalliokoski/trine)**-style [libraries](https://github.com/roobie/mori-ext), you can’t use arrow functions because they inherit `this` from the outer scope.

So a good old anonymous function expression:

``` js
[my, collection]::map(function() {
return !!this;
});
```

…often feels more natural than inventing obscure names:

``` js
[my, collection]::map(function justCastToBoolean() {
return !!this;
});
```

Start with packages/eslint-config-airbnb/.eslintrc at the linked rule around line 140, then inspect the surrounding function-naming configuration and any related style-guide documentation. Compare its behavior for ordinary anonymous functions with the bind-syntax example; done means the intended exception is defined clearly and the relevant configuration or documentation reflects it.

Written by the indexing model from the issue text.