v0.15.1

Changed

• 19 more write calls are verified live on a test administration:
  subscription lines and restrictions, bank allocation rules (beta), G/L
  account classification mappings, mailboxes, complaints, service requests
  and purchase returns (262 in all).

Fixed

• create, update and delete with --beta validate against the beta
  record of the catalogue. A beta-only resource such as
  cashflow/AllocationRule was refused as unknown.
• A network failure names its cause, for example "Cannot reach
  https://start.exactonline.be: fetch failed: getaddrinfo ENOTFOUND ...",
  instead of a bare "fetch failed".