packaging: Automate the package release process.

This commit adds a script to automate the PyPA release of the
zulip, zulip_bots and zulip_botserver packages.

The tools/release-packages script would take care of uploading
the packages to PyPA, and push commits to both repos updating the
package versions. If you have commit access to the repos, you
can --push upstream to master. If not, then you can --push
origin to a new branch on your fork and create a PR for those
changes.

Ideally, a release shouldn't take longer than however long it
takes one to type the above command. If you have SSH set up on
GitHub, you won't need to type in your GitHub username and
password. You can also store your PyPA credentials in a file
in your home directory; it isn't very secure, but it saves
time nevertheless.

zulip_bots/setup.py

@@ -9,7 +9,12 @@ import sys
 import generate_manifest
 
 ZULIP_BOTS_VERSION = "0.3.4"
+IS_PYPA_PACKAGE = False
 
+# IS_PYPA_PACKAGE is set to True by tools/release-packages
+# before making a PyPA release.
+if not IS_PYPA_PACKAGE:
+    generate_manifest.generate_dev_manifest()
 
 # We should be installable with either setuptools or distutils.
 package_info = dict(