v0.1.0

Initial release, including:

- `getJson()` and `postForJson()` functions,
  for making GET and POST requests returning JSON data.
- path`` template literal tag function,
  for encoding request paths.
- `getResponseStatus()` function,
  for getting the HTTP status code of a response.
- `RestApiServerError`, `RestApiClientError`,
  `UnexpectedResponseStatus`, `InvalidResponseBody`,
  and `UnknownResponseError` error classes thrown by these functions.