Add ability to customize sync HTTP method, data format and payload keys

[aksalj]

Add feature for developers to specify how SMSSync communicates with their server.

By default a normal POST request is sent; I needed a PUT or POST request with messages sent in JSON format (with my own keys for the data items) to ease integration with a CouchDB web app.

[eyedol]

@aksalj This is a good feature to merge. It will give so much flexibility to developers. How well does this play with web services that have the default implementation - POST only. Is the Sync Scheme tied to a specific Sync URL?

This is a huge pull request. Could you add some test cases?

[aksalj]

@eyedol The sync scheme is URL-specific and is by default the original POST with the default payload keys (secret, from, message, message_id, sent_timestamp, sent_to); messages are sent same as before, so current web services should not notice any differences (same goes for app update).

Also, since the SyncScheme class is mostly set/get with no complex logic and is tied to the SyncUrl class, tests on SyncUrl are practically testing SyncScheme as well.

[eyedol]

@aksalj thanks for the confirmation. Looks good.

Regarding the test cases, I was asking for specific test case when say JSON and PUT has been set as the Sync Scheme.

[aksalj]

@eyedol Added a few test on the different sync schemes

[eyedol]

👍

Would be nice to have you on the CREDITS file. Could you add your details and send a pull request? Thanks.