feat!: roll-up semver-major bump

The following commit message is mostly copied from cea9063:

feat!: named exports instead of default exports

It also removes the `Codec` class and exports a plain object
instead. This has consequences for imports.

BREAKING CHANGE:

Only use names exports as default exports don't play well with
CommonJS + Typescript typing.

This means that when you use ESM imports, e.g. the raw codec is
no longer imported as

```js
import raw from 'multiformats/codecs/raw'
```

but as

```js
import * as raw from 'multiformats/codecs/raw'
```

The CJS import for codecs don't change, it's still `const raw = require('multiformats/codecs/raw`.

Though other imports change, so

```js
import CID from 'multiformats/cid'
const CID = require('multiformats/cid')
```

is now

```js
import { CID } from 'multiformats/cid'
const { CID } = require ('multiformats/cid')
```

Author: rvagg

README.md

@@ -196,4 +196,3 @@ Licensed under either of
 ### Contribution
 
 Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.
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