Include cassis

[veganstraightedge]

Or document that cassis needs to be loaded to use this library.

As far as I can tell, this line won't work unless cassis is loaded by this library or by whatever app loads this library.

https://github.com/indieweb/link-rel-parser-php/blob/master/src/IndieWeb/link_rel_parser.php#L43

[tantek]

I think a README note should suffice for now. link-rel-parser-php was intended as code sharing, not any attempt of making something standalone

[veganstraightedge]

@tantek: I'll leave to you.

[tantek]

Added comments to both link_rel_parser.php and get_rel_webmention.php both explicitly documenting their dependencies on CASSIS:
https://github.com/indieweb/link-rel-parser-php/blob/master/src/IndieWeb/link_rel_parser.php#L7
https://github.com/indieweb/link-rel-parser-php/blob/master/src/IndieWeb/get_rel_webmention.php#L8

[lostfocus]

Probably wouldn't hurt to add that dependency to the composer.json.