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

log.go

@@ -0,0 +1,69 @@
+package main
+
+import (
+	"io"
+	"log"
+	"os"
+	"path/filepath"
+	"regexp"
+
+	"github.com/gin-gonic/gin"
+	"github.com/hrfee/jfa-go/linecache"
+)
+
+var logPath string = filepath.Join(temp, "jfa-go.log")
+var lineCache = linecache.NewLineCache(100)
+
+func logOutput() (closeFunc func()) {
+	old := os.Stdout
+	log.Printf("Logging to \"%s\"", logPath)
+	writers := []io.Writer{old, colorStripper{lineCache}}
+	wExit := make(chan bool)
+	r, w, _ := os.Pipe()
+	if TRAY {
+		f, err := os.OpenFile(logPath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
+		if err != nil {
+			closeFunc = func() {}
+			return
+		}
+		writers = append(writers, colorStripper{f})
+		closeFunc = func() {
+			w.Close()
+			<-wExit
+			f.Close()
+		}
+	} else {
+		closeFunc = func() {
+			w.Close()
+			<-wExit
+		}
+	}
+	writer := io.MultiWriter(writers...)
+	os.Stdout, os.Stderr = w, w
+	log.SetOutput(writer)
+	gin.DefaultWriter, gin.DefaultErrorWriter = writer, writer
+	go func() {
+		io.Copy(writer, r)
+		wExit <- true
+	}()
+	return
+}
+
+// Regex that removes ANSI color escape sequences. Used for outputting to log file and log cache.
+var stripColors = func() *regexp.Regexp {
+	r, err := regexp.Compile("\\x1b\\[[0-9;]*m")
+	if err != nil {
+		log.Fatalf("Failed to compile color escape regexp: %v", err)
+	}
+	return r
+}()
+
+type colorStripper struct {
+	file io.Writer
+}
+
+func (c colorStripper) Write(p []byte) (n int, err error) {
+	_, err = c.file.Write(stripColors.ReplaceAll(p, []byte("")))
+	n = len(p)
+	return
+}