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>

modules/print/markdown.go

@@ -6,15 +6,27 @@ package print
 
 import (
 	"fmt"
+	"os"
 
 	"github.com/charmbracelet/glamour"
+	"golang.org/x/crypto/ssh/terminal"
 )
 
 // outputMarkdown prints markdown to stdout, formatted for terminals.
 // If the input could not be parsed, it is printed unformatted, the error
 // is returned anyway.
-func outputMarkdown(markdown string) error {
-	out, err := glamour.Render(markdown, "auto")
+func outputMarkdown(markdown string, baseURL string) error {
+	renderer, err := glamour.NewTermRenderer(
+		glamour.WithAutoStyle(),
+		glamour.WithBaseURL(baseURL),
+		glamour.WithWordWrap(getWordWrap()),
+	)
+	if err != nil {
+		fmt.Printf(markdown)
+		return err
+	}
+
+	out, err := renderer.Render(markdown)
 	if err != nil {
 		fmt.Printf(markdown)
 		return err
@@ -22,3 +34,18 @@ func outputMarkdown(markdown string) error {
 	fmt.Print(out)
 	return nil
 }
+
+// stolen from https://github.com/charmbracelet/glow/blob/e9d728c/main.go#L152-L165
+func getWordWrap() int {
+	fd := int(os.Stdout.Fd())
+	width := 80
+	if terminal.IsTerminal(fd) {
+		if w, _, err := terminal.GetSize(fd); err == nil {
+			width = w
+		}
+	}
+	if width > 120 {
+		width = 120
+	}
+	return width
+}