allow unspecified arguments, fixes #484

[clavin]

Summary

Fixes #484.

This PR adds the ability to use arguments not specified in the MethodArguments types (auxiliary arguments). For example:

web.chat.postEphemeral({
    user: 'not me',
    channel: 'somewhere',
    text: 'wait, what did that say?',

    extra_argument: 'one that doesnt exist, in fact'
});

Note that this preserves static errors for missing arguments, so if channel in the above example was missing, an error will still be thrown (when using types, of course).

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #487 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #487   +/-   ##
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  Coverage   80.08%   80.08%           
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  Files           6        6           
  Lines         241      241           
  Branches       37       37           
=======================================
  Hits          193      193           
  Misses         30       30           
  Partials       18       18

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[aoberoi]

thanks so much @clavin, i'm happy with this fix. i was thinking about doing roughly the same thing. the tradeoff here is that argument names that have typos (chanel instead of channel) will not trigger an error. that's less than ideal, but i think once all the methods have an interface for their arguments, we can try to remove AuxilaryArguments (but we might want to preserve it for direct calls to .apiCall() so that can always be seen as an "escape hatch" if you know what you're doing).