Add onBufferOpen plugin callback

cmd/micro/buffer.go

@@ -8,6 +8,7 @@ import (
 	"os/exec"
 	"os/signal"
 	"path/filepath"
+	"strings"
 	"time"
 	"unicode/utf8"
 )
@@ -114,6 +115,11 @@ func NewBuffer(txt []byte, path string) *Buffer {
 		file.Close()
 	}
 
+	_, err := Call("onBufferOpen", b)
+	if err != nil && !strings.HasPrefix(err.Error(), "function does not exist") {
+		TermMessage(err)
+	}
+
 	return b
 }