Add a new adapter for Appier bidder.

[PCMan-Appier]

Type of change

• [x ] New bidder adapter

Description of change

Added a new bidder adapter for Appier.

• code: modules/appierBidAdapter.js
• doc: modules/appierBidAdapter.md
• unit test: test/spec/modules/appierBidAdapter_spec.js

• test parameters for validating bids

var adUnits = [{
    code: '/5044416/300x250_appier_prebid',  // DFP ad unit id
    mediaTypes: {
        banner: {sizes: [[300, 250]]}
    },
    bids: [{
        bidder: 'appier',
        params: {
            hzid: 'WhM5WIOp'   // appier hzid of the zone
        }
    }]
}];

pbjs.que.push(function() {
    pbjs.setConfig({
        appier: {
            'server': 'twgce-pmp-server-stg.apx.appier.net'
        }
    });
});

Be sure to test the integration with your adserver using the Hello World sample page.

• contact email of the adapter’s maintainer: apn-dev@appier.com
• [x ] official adapter submission

For any changes that affect user-facing APIs or example code documented on http://prebid.org, please provide:

• A link to a PR on the docs repo at https://github.com/prebid/prebid.github.io/: Add dev doc for Appier bidder. prebid.github.io#1058

Other information

[idettman]

You can optimize this conditional and it will behave the same:

if (!Array.isArray(serverResponse.body)) {
  return []
}

[PCMan-Appier]

@idettman I did the requested change and did git squash.
Thanks for the prompt review and the suggestions!

[idettman]

Everything looks good except for the small fix mentioned on line #64, once this is fixed I'll approve

[PCMan-Appier]

@idettman BTW, once approved, when will this be released and available from the download menu on Prebid.js official website? I mean this: http://prebid.org/download.html
Thank you.

[idettman]

LGTM