fix ValueError: Attempted relative import in non-package

README.md

@@ -38,7 +38,7 @@ $ pip install git+https://github.com/nondanee/ncmdump.git
 ### Execute
 
 ```sh
-$ ncmdump -h # equivalent to "python ncmdump/app.py -h"
+$ ncmdump -h # equivalent to "python ncmdump/app.py -h" and "python -m ncmdump.app"
 usage: ncmdump [-h] [-f format] [-o output] [-d] [-c | -r] [input [input ...]]
 
 positional arguments:

ncmdump/app.py

@@ -6,7 +6,12 @@ Created on Fri Sep 28 13:32:51 2018
 """
 
 import argparse, os, sys, traceback, re
-from .core import dump
+sys.path.append(os.path.dirname(os.path.abspath(__file__)))
+
+if __package__ is None:
+    from core import dump
+else:
+    from .core import dump
 
 parser = argparse.ArgumentParser(
     prog = 'ncmdump', add_help = False