09_git.ipynb: Beginnings of replacing '!dir'

Use pure-Python solution (using 'pathlib' module) to print the sizes of
generated files with saved commit graph in some format.

This is the beginning of replacing non-portable '!dir <directory>'
shell-out magic, and manual creation of the size tables.

Author: jnareb

09_git.ipynb

@@ -598,6 +598,64 @@
     "!dir datasets"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "['git-commit_graph.adjlist.txt.gz                    1173714',\n",
+       " 'git-commit_graph.df_edgelist.csv.gz                1629256',\n",
+       " 'git-commit_graph.df_edgelist.pickle.gz             1332691',\n",
+       " 'git-commit_graph.gexf.gz                           3063783',\n",
+       " 'git-commit_graph.gpickle.gz                        3254690',\n",
+       " 'git-commit_graph.graphml.gz                        2231397',\n",
+       " 'git-commit_graph.info.csv.gz                       3681511',\n",
+       " 'git-commit_graph.info.pickle.gz                    2833650',\n",
+       " 'git-commit_graph.pajek.gz                          1754236']"
+      ]
+     },
+     "execution_count": null,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "[\"{name:<50} {size:>7}\".format(name=p.name,size=p.stat().st_size) for p in Path(\"datasets\").glob(\"*.gz\")]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "['git-commit_graph.adjlist.txt                       2875179',\n",
+       " 'git-commit_graph.df_edgelist.csv                   4383858',\n",
+       " 'git-commit_graph.df_edgelist.feather               3857818',\n",
+       " 'git-commit_graph.df_edgelist.hdf5                  3808521',\n",
+       " 'git-commit_graph.df_edgelist.parquet               3116020',\n",
+       " 'git-commit_graph.edgelist.txt                      3692282',\n",
+       " 'git-commit_graph.hdf5                              6543155',\n",
+       " 'git-commit_graph.info.hdf5                         2735986',\n",
+       " 'git-commit_graph.info.parquet                      6079159',\n",
+       " 'git-commit_graph.multiline_adjlist.txt             3610938',\n",
+       " 'Spoon-Knife-commit_graph.adjlist.txt               15676794']"
+      ]
+     },
+     "execution_count": null,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "[\"{name:<50} {size:>7}\".format(name=p.name,size=p.stat().st_size) for p in Path(\"datasets\").iterdir() if not p.match(\"*.gz\")]"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,