Add supprot for methods containing underscore
Add supprot for methods containing underscore

It's hard to tell from reading RFC 2068 if underscores are allowed or
not in the method name. The official HTTP/1.1 methods does not contain
any underscores, but RTC 2326 (the RTSP protocol) which references the
definitions of the HTTP/1.1 RFC does (i.e. GET_PARAMETER and
SET_PARAMETER).

If would make sense ot use this module to parse RTSP headers as well, so
hence support for methods containing underscores is now added.

watson/http-headers