extend mrb file format (add filename, lines info)

extend mrb file format (lines and filename infos append to end of irep->pool).

sample source code
```
$ cat t.rb 
puts "sample"
raise "sample error"
$ ./bin/mrbc t.rb 
```

before (not output line numbers)
```
$ ./bin/mruby -b t.mrb 
sample
trace:
        [0] (unknown):-1
RuntimeError: sample error
```

after (output line numbers and original filename)
```
$ ./bin/mruby -b t.mrb 
sample
trace:
        [0] t.rb:2
t.rb:2: sample error (RuntimeError)
```