Don't count CR or LF as whitespace when trimming whitespace from header values (#306)
Don't count CR or LF as whitespace when trimming whitespace from header values (#306)

Motivation:

The OWS rule from the HTTP semantics draft only considers 'SP' and
'HTAB' to be whitespace. We also (unnecessarily) consider CR and LF to
be whitespace.

Modifications:

- Remove CR and LF from the characters we consider to be whitespace
- Update tests

Result:

We no longer consider CR or LF to be whitespace when trimming
whitespace when producing the canonical form of header values.
apple/swift-nio-http2,apple/swift-nio-http2,apple/swift-nio-http2,apple/swift-nio-http2