Accessor methods for Link Relations

[mpgirro]

#76 already proposes accessor methods for Atom link elements for RFC 5005 support. There are more link relations encountered in feeds (most are IANA registered), so I propose to extend the concept to other rel values relevant for podcast feeds. These are the link relations I know of right now:

Link Relation Type	Specification
self	RFC 4287
alternate	HTML
first	RFC 5005
last	RFC 5005
previous	RFC 5005
next	RFC 5005
prev-archive	RFC 5005
next-archive	RFC 5005
current	RFC 5005
payment	RFC 8288
hub	WebSub
http://podlove.org/simple-chapters	Podlove External Chapter Information
http://podlove.org/deep-link	Podlove Deep Linking
replies	RFC 4685
search	OpenSearch
related	RFC 4287

Accessor methods should be exposed in the Atom Link companion object. The feed history companion can then simply delegate to the Atom methods.

I'll also add this to the scrapper to find out if there are more link relations around.

[mpgirro]

Updated table with RFC 4685 "replies" relation

[mpgirro]

We can also extend this by providing creation methods in the companion for convenience:

const val SELF_REL = "self"

fun createSelfRelation(
    val href: String,
    val hrefLang: String? = null,
    val hrefResolved: String? = null,
    val length: String? = null,
    val title: String? = null,
    val type: MediaType? = null
) = Link(href, hrefLang, hrefResolved, length, title, SELF_REL, title, type)