Move version to a single file

In the previous code, the version had to be changed in two places, the
`setup.py` and `bin/ytmdl`, it's now in one file and the other files
read it from there.

bin/ytmdl

@@ -30,6 +30,7 @@ from ytmdl import (
             logger,
             stringutils,
 )
+from ytmdl.__version__ import __version__
 
 # init colorama for windows
 init()
@@ -102,7 +103,7 @@ def arguments():
                         and keep only the music in the file. Useful in songs where there \
                         are speeches, noise etc before/after the start of the song. Default \
                         is false.", action='store_true')
-    parser.add_argument('--version', action='version', version='2020.07.26',
+    parser.add_argument('--version', action='version', version=__version__,
                         help='show the program version number and exit')
 
     playlist_group = parser.add_argument_group("Playlist")

setup.py

@@ -6,6 +6,8 @@
 with open("README.md", "r") as fh:
     long_description = fh.read()
 
+exec(open("ytmdl/__version__.py").read())
+
 req_pkgs = [
             'youtube_dl',
             'mutagen',
@@ -32,7 +34,7 @@
 if __name__ == '__main__':
     setuptools.setup(
         name="ytmdl",
-        version="2020.07.26",
+        version=__version__,
         author="Deepjyoti Barman",
         author_email="[email protected]",
         description="Youtube Music Downloader",

ytmdl/__version__.py

@@ -0,0 +1,2 @@
+# Store the version of the package
+__version__ = "2020.07.26"