Handle multiple ACRH field lines

[jub0bs]

Fetch-compliant browsers send no more than one ACRH field line (see https://fetch.spec.whatwg.org/#cors-preflight-fetch-0, step 5). Accordingly, the library's middleware ignore ACRH field lines beyond the first one (if any).

However, some intermediaries may well (and some reportedly do) split that single ACRH field lines into multiple ACRH field lines. When this happens, preflight may unduly fail.

Therefore, this library should be enhanced so as to handle multiple ACRH field lines.

[jub0bs]

This feature is coming in v0.3.0.