Turn --verify=False/True to --verify=no/yes

[floer32]

One way to address #559 -- instead of warning or throwing an error, just accept "True" and "False"
as synonyms of yes/no

[jkbrzt]

@hangtwenty thanks for the pull request. I can understand the confusion. Here's a possibly more robust solution.

https://github.com/jkbrzt/httpie/blob/de38f86730bae524b9cbec317a6275a74987400a/httpie/client.py#L163

        'verify': {
            'yes': True,
            'true': True,
            'no': False,
            'false': False,
        }.get(args.verify.lower(), args.verify),