Parses a header which is a comma-delimited list of something like: token [ "=" ( token | quoted-string ) ].
Tokens that don't have an associated value will still be added to the resulting hash table, but with a null value.
This also handles RFC5987 encoding (which in HTTP is mostly used for giving UTF8-encoded filenames in the Content-Disposition header).
| header |
a header value |
|
a GenericSet of list elements, which can be freed with header_free_param_list. |