v1.4.0

Fixes from running the library over public SDP sets; see "Checked against public SDP sets" in
the README.

Added

• yarn check:external runs the library over public collections and captures, downloaded into
  .cache/. It is a manual check, not part of the tests or CI, and none of the data is in this
  repository.

Fixed

• sdpReader.parse accepted an m= line with an empty media type, proto or non-RTP format
  (m=audio 9 RTP/AVP 0 gave proto: "" and lost the codecs). It now throws
  expected "<media> <port> <proto> <fmt> ...". Strict mode rejects input it used to accept.
• sdpReader.parseLenient: doubled spaces in a malformed m= line shifted the fields
  (m=audio 9 RTP/AVP 0 gave proto: "9" and no port) or left '' in formats.
• sdpReader.isComplete is false for a media section without formats (m=video 0 RTP/AVP),
  which sdpWriter.write refuses.