Accept headers without spaces
Accept headers without spaces

YaHTTP did not accept a header like

```
Accept:application/json
```

Which should be allowed according to RFC 7230:

> Each header field consists of a case-insensitive field name
> followed by a colon (":"), optional leading whitespace, the
> field value, and optional trailing whitespace.

cmouse/yahttp,cmouse/yahttp,cmouse/yahttp