add REST documentation for mediacore module

Looks like the API is wrong. Here's the returned object from a Mediacore embed on production:

```
{
    "url": "https://gatech.mediacore.tv/media/oae-usability-tests_xaiver_20140408mov/embed_player?iframe=True",
    "html": "<iframe src=\"https://gatech.mediacore.tv/media/oae-usability-tests_xaiver_20140408mov/embed_player?iframe=True&_Policy=eyJyZXNvdXJjZSI6Imh0dHBzOi8vZ2F0ZWNoLm1lZGlhY29yZS50di9tZWRpYS9vYWUtdXNhYmlsaXR5LXRlc3RzX3hhaXZlcl8yMDE0MDQwOG1vdi9lbWJlZF9wbGF5ZXIiLCJxdWVyeV9zdHJpbmciOiJpZnJhbWU9VHJ1ZSIsImV4cGlyeV9lcG9jaCI6MTQwNTM2MjAxMH0&_Signature=cYqehKVOvf2W0gxBL2Xl4n3XVva2qzBH5CbvD7rWPwBVmZtlgCQXCf0hCjp0jhEucPne20TkH_TDAbSECUPgYw&_KeyId=Bl6tl09HMMw\" mozallowfullscreen=\"mozallowfullscreen\" webkitallowfullscreen=\"webkitallowfullscreen\" width=\"400\" allowfullscreen=\"allowfullscreen\" height=\"225\" scrolling=\"no\" frameborder=\"0\"></iframe>"
}
```