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

linecache/linecache_test.go

@@ -0,0 +1,17 @@
+package linecache
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+	"time"
+)
+
+func Test(t *testing.T) {
+	wr := NewLineCache(10)
+	for i := 10; i < 50; i++ {
+		fmt.Fprintln(wr, i)
+		fmt.Print(strings.ReplaceAll(wr.String(), "\n", " "), "\n")
+		time.Sleep(time.Second)
+	}
+}