feat: allow parse with no arguments as alias for yargs.argv

[bcoe]

I showed the the proposed promise API for yargs to several coworkers today at npm, and they managed to talk me out of it. Their reasoning being:

1. yargs is for the most part a synchronous API, and they didn't see much value in introducing the deferred behavior.
2. my coworker @zkat felt that the method name .then() felt weird; this method name should be used internally by the Promise api, not by APIs exposing a promise.

Rather than introducing a new method run() (or the method I recommended then() for exposing a Promise), I feel a good compromise is to instead extend the method parse() which already exists in the API. Calling:

require('yargs')
  .option('x', {describe: 'x option'})
  .parse()

is now possible, and is equivalent to:

require('yargs')
  .option('x', {describe: 'x option'})
  .argv

I like this approach: it gets around the linting warning now frequently triggered by .argv, and avoids adding a new method to yargs' already large API surface.

We definitely might revisit a Promise-based API in the future, one recommendation made by my coworker @chrisdickinson was to make yargs' command API promise based, e.g.,

• a command would return a promise to execute.
• yargs would return a promise that resolves once the command is completed.

[bernardmcmanus]

👍 this feels much cleaner

[bcoe]

@bernardmcmanus going to do my best to get this out today.

[bcoe]

@bernardmcmanus I've released this work in yargs@next would love your help testing if you have a few moments:

npm i yargs@next