Detect markdown line width, resolve relative URLs (#332)

~~this is semi-blocked by https://github.com/charmbracelet/glamour/pull/96, but behaviour isn't really worse than the previous behaviour (most links work, some are still broken)~~

#### testcase for link resolver
```
tea pr 332
tea checkout 332 && make install && tea pr 332
```

- [rel](./332)
- [abs](/gitea/tea/pulls/332)
- [full](https://gitea.com/gitea/tea/pulls/332)

Co-authored-by: Norwin Roosen <git@nroo.de>
Co-authored-by: 6543 <6543@obermui.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/332
Reviewed-by: 6543 <6543@obermui.de>
Reviewed-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Norwin <noerw@noreply.gitea.io>
Co-committed-by: Norwin <noerw@noreply.gitea.io>

vendor/github.com/yuin/goldmark-emoji/README.md

@@ -0,0 +1,71 @@
+goldmark-emoji
+=========================
+
+[![GoDev][godev-image]][godev-url]
+
+[godev-image]: https://pkg.go.dev/badge/github.com/yuin/goldmark-emoji
+[godev-url]: https://pkg.go.dev/github.com/yuin/goldmark-emoji
+
+goldmark-emoji is an extension for the [goldmark](http://github.com/yuin/goldmark) 
+that parses `:joy:` style emojis.
+
+Installation
+--------------------
+
+```
+go get github.com/yuin/goldmark-emoji
+```
+
+Usage
+--------------------
+
+```go
+import (
+    "bytes"
+    "fmt"
+
+    "github.com/yuin/goldmark"
+    "github.com/yuin/goldmark-emoji"
+    "github.com/yuin/goldmark-emoji/definition"
+)
+
+func main() {
+    markdown := goldmark.New(
+        goldmark.WithExtensions(
+            emoji.Emoji,
+        ),
+    )
+    source := `
+    Joy :joy:
+    `
+    var buf bytes.Buffer
+    if err := markdown.Convert([]byte(source), &buf); err != nil {
+        panic(err)
+    }
+    fmt.Print(buf.String())
+}
+```
+
+See `emoji_test.go` for detailed usage.
+
+### Options
+
+Options for the extension
+
+| Option | Description |
+| ------ | ----------- |
+| `WithEmojis` | Definition of emojis. This defaults to github emoji set |
+| `WithRenderingMethod` | `Entity` : renders as HTML entities, `Twemoji` : renders as an img tag that uses [twemoji](https://github.com/twitter/twemoji), `Func` : renders using a go function |
+| `WithTwemojiTemplate` | Twemoji img tag printf template |
+| `WithRendererFunc` | renders by a go function |
+
+
+
+License
+--------------------
+MIT
+
+Author
+--------------------
+Yusuke Inuzuka
+