add REST documentation for content module

Here's a response from a POST to `api/content/contentId` to change the metadata. But contrary to the comment above, I don't think it's a `BasicContent` object. Looks like the full profile to me.

```
{
  "tenant": {
    "alias": "Tenant",
    "displayName": "Tenant"
  },
  "id": "c:Tenant:eyxafW6Ige",
  "visibility": "loggedin",
  "displayName": "paper.pdf",
  "description": "New Description",
  "resourceSubType": "file",
  "createdBy": {
    "tenant": {
      "alias": "Tenant",
      "displayName": "Tenant"
    },
    "id": "u:Tenant:xylrEJMQDp",
    "displayName": "User One",
    "visibility": "public",
    "email": "userone@not.iz",
    "locale": "en_US",
    "publicAlias": "User One",
    "picture": {
      "small": "/api/download/signed?uri=local%3Au%2FTenant%2Fxy%2Flr%2FEJ%2FMQ%2FxylrEJMQDp%2Fprofilepictures%2F1405435284144%2Fsmall.jpg&expires=1407974400000&signature=0c49333b018eba38d66ee60f93678eb7fffe61ef",
      "medium": "/api/download/signed?uri=local%3Au%2FTenant%2Fxy%2Flr%2FEJ%2FMQ%2FxylrEJMQDp%2Fprofilepictures%2F1405435284144%2Fmedium.jpg&expires=1407974400000&signature=ac86178a70edd139241d07c9f392ff486e556a99",
      "large": "/api/download/signed?uri=local%3Au%2FTenant%2Fxy%2Flr%2FEJ%2FMQ%2FxylrEJMQDp%2Fprofilepictures%2F1403542881749%2Flarge.jpg&expires=1407974400000&signature=81c28208a86b0f7aaaab42503a3df9c77fcf0478"
    },
    "profilePath": "/user/Tenant/xylrEJMQDp",
    "resourceType": "user",
    "notificationsUnread": 2,
    "notificationsLastRead": 1407260686952,
    "acceptedTC": 1400523404749,
    "lastModified": 1407261037323,
    "emailPreference": "daily"
  },
  "created": "1403697261908",
  "lastModified": "1407264767569",
  "profilePath": "/content/Tenant/eyxafW6Ige",
  "resourceType": "content",
  "latestRevisionId": "rev:Tenant:Wkhv3ZZHW",
  "previews": {
    "cssScopeClass": "c-Tenant-eyxafW6Ige-rev-Tenant-Wkhv3ZZHW-pdf2html",
    "pageCount": 14,
    "status": "done",
    "total": 20,
    "thumbnailUrl": "/api/download/signed?uri=local%3Ac%2FTenant%2Fey%2Fxa%2FfW%2F6I%2FeyxafW6Ige%2Fpreviews%2Frev-Tenant-Wkhv3ZZHW%2Fthumbnail.jpg&expires=1407974400000&signature=c0bb5cb2cf5a434eca7d6def2083baa4535de66b",
    "smallUrl": "/api/download/signed?uri=local%3Ac%2FTenant%2Fey%2Fxa%2FfW%2F6I%2FeyxafW6Ige%2Fpreviews%2Frev-Tenant-Wkhv3ZZHW%2Fsmall.png&expires=1407974400000&signature=9fefc3460a621b5a702dbb0cc4770124822f087c",
    "mediumUrl": "/api/download/signed?uri=local%3Ac%2FTenant%2Fey%2Fxa%2FfW%2F6I%2FeyxafW6Ige%2Fpreviews%2Frev-Tenant-Wkhv3ZZHW%2Fmedium.png&expires=1407974400000&signature=6f552b162a0327e5cafe9a8a831685413cff677b",
    "largeUrl": "/api/download/signed?uri=local%3Ac%2FTenant%2Fey%2Fxa%2FfW%2F6I%2FeyxafW6Ige%2Fpreviews%2Frev-Tenant-Wkhv3ZZHW%2Flarge.png&expires=1407974400000&signature=b14abdeb1f54ddaefc495ce516919f7b20654500",
    "wideUrl": "/api/download/signed?uri=local%3Ac%2FTenant%2Fey%2Fxa%2FfW%2F6I%2FeyxafW6Ige%2Fpreviews%2Frev-Tenant-Wkhv3ZZHW%2Fwide.jpg&expires=1407974400000&signature=b100bdea07a650783b7045d8098fc8e6271f95c3"
  },
  "downloadPath": "/api/content/c:Tenant:eyxafW6Ige/download/rev:Tenant:Wkhv3ZZHW",
  "filename": "paper.pdf",
  "size": 1016315,
  "mime": "application/pdf",
  "signature": {
    "expires": 1407326400000,
    "signature": "ba16f69f74f3103b84f369b2fbed2ccde637ae22"
  },
  "isManager": true,
  "canShare": true
}
```

Here's the response to publishing a collabdoc:

```
{
  "tenant": {
    "alias": "Tenant",
    "displayName": "Tenant"
  },
  "id": "c:Tenant:ZytOGdxrb",
  "visibility": "public",
  "displayName": "Test",
  "description": "",
  "resourceSubType": "collabdoc",
  "createdBy": "u:Tenant:lkluiO1Cua",
  "created": "1407260720910",
  "lastModified": "1407260795690",
  "profilePath": "/content/Tenant/ZytOGdxrb",
  "resourceType": "content",
  "latestRevisionId": "rev:Tenant:WkIvS_lBZ",
  "previews": {
    "status": "done",
    "total": 2,
    "thumbnailUrl": "/api/download/signed?uri=local%3Ac%2FTenant%2FZy%2FtO%2FGd%2Fxr%2FZytOGdxrb%2Fpreviews%2Frev-Tenant-WkIvS_lBZ%2Fthumbnail.png&expires=1407974400000&signature=09dcd4cbfb9df9dff82b3cec03a17002698b0ebe",
    "wideUrl": "/api/download/signed?uri=local%3Ac%2FTenant%2FZy%2FtO%2FGd%2Fxr%2FZytOGdxrb%2Fpreviews%2Frev-Tenant-WkIvS_lBZ%2Fwide.png&expires=1407974400000&signature=212f13b2c0eff4c3f33e031b4c06b2df705b206a"
  },
  "etherpadGroupId": "g.t0Ksj73idCX2TbcE",
  "etherpadPadId": "g.t0Ksj73idCX2TbcE$c_Tenant_ZytOGdxrb",
  "signature": {
    "expires": 1407326400000,
    "signature": "efa7967757af0caf46c4135fcbf8f832c9b482a3"
  },
  "latestRevision": {
    "revisionId": "rev:Tenant:WkIvS_lBZ",
    "contentId": "c:Tenant:ZytOGdxrb",
    "created": "1407260795684",
    "createdBy": "u:Tenant:lkluiO1Cua",
    "etherpadHtml": "neWelcome to Etherpad!<br><br>This pad text is synchronized as you type, so that everyone viewing this page sees the same text. This allows you to collaborate seamlessly on documents!<br><br>Get involved with Etherpad at <a href=\"http&#x3a;&#x2F;&#x2F;etherpad&#x2e;org\">http:&#x2F;&#x2F;etherpad.org</a><br><br>",
    "previews": {
      "wideUri": "local:c/Tenant/Zy/tO/Gd/xr/ZytOGdxrb/previews/rev-Tenant-WkIvS_lBZ/wide.png",
      "status": "done",
      "total": 2,
      "thumbnailUri": "local:c/Tenant/Zy/tO/Gd/xr/ZytOGdxrb/previews/rev-Tenant-WkIvS_lBZ/thumbnail.png"
    },
    "previewsId": "rev:Tenant:WkIvS_lBZ",
    "status": "done",
    "wideUri": "local:c/Tenant/Zy/tO/Gd/xr/ZytOGdxrb/previews/rev-Tenant-WkIvS_lBZ/wide.png",
    "thumbnailUrl": "/api/download/signed?uri=local%3Ac%2FTenant%2FZy%2FtO%2FGd%2Fxr%2FZytOGdxrb%2Fpreviews%2Frev-Tenant-WkIvS_lBZ%2Fthumbnail.png&expires=1407974400000&signature=09dcd4cbfb9df9dff82b3cec03a17002698b0ebe"
  }
}
```

And here's the response to a POST to restore a revision:

```
{
  "contentId": "c:Tenant:eyxafW6Ige",
  "created": "1407265095934",
  "createdBy": "u:Tenant:xylrEJMQDp",
  "filename": "paper.pdf",
  "mime": "application/pdf",
  "previews": {
    "cssScopeClass": "c-Tenant-eyxafW6Ige-rev-Tenant-Wkhv3ZZHW-pdf2html",
    "pageCount": 14,
    "smallUri": "local:c/Tenant/ey/xa/fW/6I/eyxafW6Ige/previews/rev-Tenant-Wkhv3ZZHW/small.png",
    "wideUri": "local:c/Tenant/ey/xa/fW/6I/eyxafW6Ige/previews/rev-Tenant-Wkhv3ZZHW/wide.jpg",
    "largeUri": "local:c/Tenant/ey/xa/fW/6I/eyxafW6Ige/previews/rev-Tenant-Wkhv3ZZHW/large.png",
    "mediumUri": "local:c/Tenant/ey/xa/fW/6I/eyxafW6Ige/previews/rev-Tenant-Wkhv3ZZHW/medium.png",
    "status": "done",
    "total": 20,
    "thumbnailUri": "local:c/Tenant/ey/xa/fW/6I/eyxafW6Ige/previews/rev-Tenant-Wkhv3ZZHW/thumbnail.jpg"
  },
  "previewsId": "rev:Tenant:Wkhv3ZZHW",
  "size": "1016315",
  "status": "done",
  "uri": "local:c/Tenant/ey/xa/fW/6I/eyxafW6Ige/rev-Tenant-Wkhv3ZZHW/paper.pdf",
  "wideUri": "local:c/Tenant/ey/xa/fW/6I/eyxafW6Ige/previews/rev-Tenant-Wkhv3ZZHW/wide.jpg",
  "revisionId": "rev:Tenant:Z1evpzZSW",
  "downloadPath": "/api/content/c:Tenant:eyxafW6Ige/download/rev:Tenant:Z1evpzZSW",
  "thumbnailUrl": "/api/download/signed?uri=local%3Ac%2FTenant%2Fey%2Fxa%2FfW%2F6I%2FeyxafW6Ige%2Fpreviews%2Frev-Tenant-Wkhv3ZZHW%2Fthumbnail.jpg&expires=1407974400000&signature=c0bb5cb2cf5a434eca7d6def2083baa4535de66b",
  "mediumUrl": "/api/download/signed?uri=local%3Ac%2FTenant%2Fey%2Fxa%2FfW%2F6I%2FeyxafW6Ige%2Fpreviews%2Frev-Tenant-Wkhv3ZZHW%2Fmedium.png&expires=1407974400000&signature=6f552b162a0327e5cafe9a8a831685413cff677b"
}
```

So they're definitely different