This has two advantages;
* We can split bugdown/__init__.py into several modules, and each
module can access these arguments by importing these
* We get rid of the super-ugly `global db_data` construct, replacing
it with a only slightly ugly monkey-ish patching of the
`zerver.lib.bugdown.arguments` module, which is at least
considerably more clear on reading as to what it's purpose is.
Shubham Dhama