Auto merge of #45 - danlrobertson:tex_image, r=metajack
Auto merge of #45 - danlrobertson:tex_image, r=metajack

Implement copyTexImage2D, copyTexSubImage2D and texSubImage2D

Implement copyTexImage2D, copyTexSubImage2D and texSubImage2D and add rules to the `.gitignore` for vim users. Let me know if I missed anything!

Blocked by: servo/gleam#80

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/webrender_traits/45)
<!-- Reviewable:end -->

alanamramjit/webrender,servo/webrender,servo/webrender,servo/webrender_traits,DDEFISHER/webrender_traits,servo/webrender,servo/webrender,alanamramjit/webrender,servo/webrender,servo/webrender