Rewrite `import` statements

Nobody has claimed this yet.

At the very least, raw imports can be done easily:

```js
import foo from 'bar';
//=> var foo = require('bar');
```

Handling multiple and/or partial imports will be more problematic:

```js
import { foo, bar } from 'baz';
//=> var foo = require('baz').foo;
//=> var bar = require('baz').bar;
```

Handling aliases is the next step:

```js
import * as foo from 'bar';
//=> var foo = require('bar');

import { foo as bar } from 'baz';
//=> var bar = require('baz').bar;
```

### Concerns

* Handling `default` exports (╯°□°）╯

---

#### References

#4, https://github.com/flyjs/fly/issues/239, https://github.com/flyjs/fly/issues/159#issuecomment-208233654

Start by reviewing the import examples in this issue, then read referenced issues #4, Fly #239, and Fly #159. Define the supported raw, partial, aliased, and default-import cases, and verify that the rewrite handles each documented form consistently.

Written by the indexing model from the issue text.