Generate crash report txt and webpage

The last 100 lines of logs are now cached, and when a crash occurs, they
are saved to a file in the temp directory ("/tmp" on *nix), and pretty
HTML version is also created and opened in the browser.
* Currently only handles panics, will be included in more places soon
* Copy button and button to generate a GH issue will be added

exit.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"html/template"
+	"log"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/pkg/browser"
+)
+
+// Exit dumps the last 100 lines of output to a crash file in /tmp (or equivalent), and generates a prettier HTML file containing it that is opened in the browser if possible.
+func Exit(err interface{}) {
+	tmpl, err2 := template.ParseFS(localFS, "html/crash.html", "html/header.html")
+	if err2 != nil {
+		log.Fatalf("Failed to load template: %v", err)
+	}
+	logCache := lineCache.String()
+	data := map[string]interface{}{
+		"Log": logCache,
+	}
+	if err != nil {
+		data["Err"] = err
+	}
+	fpath := filepath.Join(temp, "jfa-go-crash-"+time.Now().Local().Format("2006-01-02T15:04:05"))
+	err2 = os.WriteFile(fpath+".txt", []byte(logCache), 0666)
+	if err2 != nil {
+		log.Fatalf("Failed to write crash dump file: %v", err2)
+	}
+	f, err2 := os.OpenFile(fpath+".html", os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
+	if err2 != nil {
+		log.Fatalf("Failed to open crash dump file: %v", err2)
+	}
+	defer f.Close()
+	err2 = tmpl.Execute(f, data)
+	if err2 != nil {
+		log.Fatalf("Failed to execute template: %v", err2)
+	}
+	browser.OpenFile(fpath + ".html")
+}