Added URL Suffixes to Resources

[matsko]

When using AngularJS with a server-side framework that requires a URL suffix like .json then angular will keep the suffix for all resource variants. So when you have a POST or index request then you end up having URLs that look like "/resource/.json".

Here's the issue in detail:
http://stackoverflow.com/questions/11622665/format-all-model-service-urls-to-include-json-in-angular-js

I've added the code into the repo to fix this. By setting a _suffix variable in the params{} hash when creating a resource then the suffix can be added properly.

[mhevery]

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[pkozlowski-opensource]

@matsko Thank you for your contribution! You've got a valid point that the current $resource doesn't support suffixes.

Unfortunately your pull request can't be merged as is (see my comments for the individual commits). You would need to do:

• remove changes to the README.md
• add tests
• add documentation
• rebase your changes on the current master (there were some changes in the $resource)

You will also have to sign the CLA as requested by @mhevery , without the CLA signed you PR can't be merged.

[pkozlowski-opensource]

@matsko We haven't heard from you for a while so I'm going to close this PR. Please re-open it when you've got time working on it and address issues listed above.