(web response) and (web request): bodies are bytevectors

(web response) and (web request): bodies are bytevectors

* module/web/request.scm (read-request-body, write-request-body): Rename
  from read-request-body/bytevector and
  write-request-body/bytevector.  Remove the /latin-1 variants, as they
  were unused and a bad idea.
* module/web/response.scm (read-response-body, write-response-body):
  Likewise.

* module/web/server/http.scm (http-read, http-write): Adapt to
  request/response change.

* test-suite/tests/web-request.test:
* test-suite/tests/web-response.test: Update tests.