implement github style link headers

[ashleygwilliams]

fixes #224

to do:

• update tests
• clean up util

[revin]

It occurred to me while doing something else that we can eliminate savedTokenConstructor from this file and just do

if (!Token) {
  Token = state.Token
  tokenUtil.set(Token)
}

[ashleygwilliams]

I LOVE DELETING CODE

[ashleygwilliams]

119 passing (4s)
  33 failing

[revin]

33, wow. I guess that part of the rendering is well covered 😛

[revin]

✨152 passing ✨

[ashleygwilliams]

niiiiiiiice 👯

[ashleygwilliams]

thought -> should the SVG icon be a flag? @revin

[revin]

@ashleygwilliams probably, you're right. We have a slightly now misnamed option prefixHeadingIds that enables or disables the 'user-content-' string that gets prepended to the generated <a> ids, but nothing for skipping the heading processing completely.

Want an option that disables the link generation altogether? Or an option that enables it, default true, and you can set it to false manually if you want? Basically we would be allowing folks to completely skip our githubHeadings plugin completely.

Also since this is already semver-major, should we rename prefixHeadingIds to be more accurate? Something like ... prefixHeadingLinkIds ...? I don't know, seems long, and you could argue that conceptually the IDs are for the headings, just not the <h1>, <h2>, etc. elements themselves. I think I just talked myself into leaving that alone.

[revin]

Oh wait, did you mean disabling just the icon itself, but still doing the rest of the processing (so we'd still generate the slug and link, but the link would be empty)?

[ashleygwilliams]

hah yes, the second thing, just the SVG part. something like --without-icons

[revin]

I added this as options.enableHeadingLinkIcons for programmatic usage; maybe we could add the CLI part in #132?