Expose EmbeddedResourceLoader to c api

[NickSpag]

Background

This PR exposes the c api to the EmbeddedResourceLoader, to prevent some of the issues mentioned here.

Approach

• Followed PFFilesystemResourceLoaderLocate and simply exposed the ERL's new and boxed it in the ResourceLoaderWrapper
• Used the Create terminology in the signature to match the rest of the api where a new() is called

Notes

• I successfully tested it in a little .NET binding project I'm working on.
• Moved the `gl` section comment down with the GL methods, as it seemed a little out of place. added a `resources` one. then moved the destroy fn in to the new section.

Let me know if I misinterpreted anything or if there are any changes, stylistic or otherwise, that you'd prefer. Thanks!

[pcwalton]

@bors-servo: r+

[bors-servo]

📌 Commit 04787f1 has been approved by pcwalton

[bors-servo]

⌛ Testing commit 04787f1 with merge a51176a...

[pcwalton]

Looks great, thanks!

[bors-servo]

☀️ Test successful - checks-travis
Approved by: pcwalton
Pushing a51176a to master...