5.0.0 Major Release

tl;dr unless you are checking/validating the types or messages of errors thrown by arg, it is safe to upgrade with no changes to your codebase. In such cases, arg will behave exactly the same as the previous version.

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Despite the major release bump, the changes here should affect only the most remote corner cases. Nonetheless, this release was a major bump out of an abundance of caution.

• All errors are now of type require('arg').ArgError. All arg-related (non-TypeError) errors are an instance of this class, and each has a .code property with a unique arg-related failure. All errors relating to the configuration of arg itself (and thus cannot be fixed by changing user input) begin with ARG_CONFIG_. The circumstances under which the errors are thrown, or the variety of errors, remain unchanged.
• All errors now start with a lowercase letter instead of an uppercase letter to match common Node.js convention.
• The CircleCI badge image and link were fixed.
• All mentions of "ZEIT" were changed to "Vercel" (https://vercel.com/blog/zeit-is-now-vercel)
• Copyright date and associated name were updated

If any of these changes have broken you in any way, feel free to open an issue on the arg issue tracker.