v0.2.0

- Major functionality update: beyond `getJson()` and `postForJson()`,
  m3api-rest now supports the following:
    - request methods:
      - GET
      - POST
      - PUT
      - DELETE
      - PATCH
    - request body content types:
      - `application/json`
      - `application/x-www-form-urlencoded`
      - `multipart/form-data`
    - response body content types:
      - `application/json`
      - `text/plain`
      - `text/html`
  Yielding the following full list of request functions:
    - `getJson()`
    - `getText()`
    - `getHtml()`
    - `postForJson()`
    - `postForText()`
    - `postForHtml()`
    - `putForJson()`
    - `putForText()`
    - `putForHtml()`
    - `deleteForJson()`
    - `deleteForText()`
    - `deleteForHtml()`
    - `patchForJson()`
    - `patchForText()`
    - `patchForHtml()`
- BREAKING CHANGE: `getJson()` and `postForJson()` can now return
  `String` instances in addition to objects and arrays, if the server
  returns JSON-encoded strings. (This is unlikely for MediaWiki core’s
  REST API endpoints, but common in the Wikibase REST API.)
- BREAKING CHANGE: The `body` property of the `RestApiServerError`,
  `RestApiClientError` and `UnexpectedResponseStatus` classes is now
  documented with the type `*` (“any”) rather than `string|Object`. The
  previous type was incorrect – if the server response is JSON,
  m3api-rest just decodes it for the error without checking if it’s an
  object or not. (You almost certainly don’t need to care about this
  change, but it’s technically breaking.)