Encode via command line cannot set headers

[Botono]

There is no way to set headers on a token when encoding via the command line.

Expected Result

Command line arguments should accept some kind of headers input and pass it to encode().

Actual Result

Headers cannot be set.

Reproduction Steps

pyjwt --key=secret --alg='RS256' encode iss=issuer aud=audience sub=subject exp=123456789 headers=foo

headers value will appear in the payload.

You can see that no header value is passed to encode() here:

pyjwt/jwt/__main__.py

Lines 46 to 50 in 6845515

	token = encode(
	payload,
	key=args.key,
	algorithm=args.algorithm
	)

But encode() supports header information:

pyjwt/jwt/api_jwt.py

Line 45 in 6845515

headers=None, # type: Optional[Dict]

System Information

$ python -m jwt.help

{
  "cryptography": {
    "version": "2.6.1"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.7.0"
  },
  "platform": {
    "release": "17.7.0",
    "system": "Darwin"
  },
  "pyjwt": {
    "version": "1.7.1"
  }
}

[jpadilla]

@Botono wanna put together a pull request?

[justinbaur]

I'd like to help out with this.

[jpadilla]

@justinbaur that'd be awesome, thanks!

[benclark0]

Is there any chance you'd consider making a new version with this change? It'd make my life considerably easier.