Add `help_url`; Allow user to turn off automatic updates

Developer can specify a `help_url` when instantiating `Workflow`.

If the workflow throws an error, this URL will be displayed in the log/Alfred debugger.

It can also be opened directly by the user with `workflow:help`

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Users can toggle automatic update checks with `workflow:noautoupdate` and workflow:autoupdate`
Add `Workflow.dumbify_punctuation()` to replace smart quotes and dashes
Change encoding test URLs
Make magic args configurable

The prefix can now be changed via `Workflow.magic_prefix`
Existing magic args can be altered or new ones added via `Workflow.magic_arguments` dict