add bundle.py to create single-file bbj client

python is able to import modules from a zip file. if the zip file
contains __main__.py it will even run it as a script! this lets us bundle
bbj's frontend together with its sole external dependency (urwid) to
create a single executable file that'll run anywhere with python
installed, no virtualenv needed.

the only downside is that python can't import shared objects (.so) from a
zip file, so urwid can't use its C-accelerated str_util module and has
to fall back to the python version. which is slower, probably.

bundle.py

@@ -0,0 +1,32 @@
+import zipfile
+import glob
+import os
+
+
+# TODO: should we include .pyc files?
+# TODO: add urwid source into the repo somewhere
+
+files = {
+    '__main__.py': 'clients/urwid/main.py',
+    'network.py': 'clients/network_client.py',
+    'urwid': 'env/lib/python3.8/site-packages/urwid/*.py',
+}
+
+with open('bbj_demo', 'wb') as f:
+    f.write(b"#!/usr/bin/env python3\n")
+    with zipfile.ZipFile(f, 'w', compression=zipfile.ZIP_DEFLATED) as z:
+        z.comment = b'BBJ'
+        for name, source in files.items():
+            if '*' in source:
+                dirname = name
+                for path in sorted(glob.glob(source)):
+                    name = dirname + '/' + os.path.basename(path)
+                    z.write(path, name)
+            else:
+                z.write(source, name)
+try:
+    mask = os.umask(0)
+    os.umask(mask)
+except OSError:
+    mask = 0
+os.chmod(z.filename, 0o777&~mask)