Add Opengl documentation (gl4 + gl2.1)

[Suraj-Yadav]

If you're adding a new scraper, please ensure that you have:

• [x] Tested the scraper on a local copy of DevDocs
• [x] Ensured that the docs are styled similarly to other docs on DevDocs

• [x] Added these files to the public/icons/your_scraper_name/ directory:
  • [x] 16.png: a 16×16 pixel icon for the doc
  • [x] [email protected]: a 32×32 pixel icon for the doc
  • [x] SOURCE: A text file containing the URL to the page the image can be found on or the URL of the original image itself

[Suraj-Yadav]

@simon04 I have implemented the requested changes.

[Suraj-Yadav]

Hi @simon04, Can this be looked into again?