(feat) Support LF separators since rfc7230-3.5 allows for LF-only

[leonardb]

   the sequence CRLF, a recipient MAY recognize a single LF as a line
   terminator and ignore any preceding CR.```

I'm running into this issue with an SMS service provider's API where all responses use LF instead of CRLF in the headers.

[leonardb]

Seems CI system is broken Could not find suitable distribution for Requirement.parse('cffi>=1.0.0')