Disallow HTML img tags and require markdown image links

[axic]

These are the current users of this feautre:

eip-1822.md:<p align="center"><img src="../assets/eip-1822/proxy-diagram.png" alt="diagram" width="600"/></p>
eip-2255.md:  <img src="../assets/eip-2255/facebook_permissions.png" alt="Facebook Permissions" />
eip-2255.md:  <img src="../assets/eip-2255/log_in_with_apple.jpeg" alt="Log in With Apple" />
eip-2535.md:<img align="right" src="../assets/eip-2535/diamond.svg" width="230" height="230">
eip-2535.md:<img src="../assets/eip-2535/DiamondDiagram.png">
eip-2535.md:<img src="../assets/eip-2535/diamondstorage1.png">
eip-2535.md:<img src="../assets/eip-2535/facetreuse.png">
eip-712.md:<img src="https://github.com/ethereum/EIPs/blob/master/assets/eip-712/eth_sign.png?raw=true" style="padding-bottom: 20px; padding-top: 20px" width="60%" />
eip-712.md:<img src="https://github.com/ethereum/EIPs/blob/master/assets/eip-712/eth_signTypedData.png?raw=true" style="padding-bottom: 20px; padding-top: 20px" width="60%" />

I wonder if we should also aim to disallow HTML tags in general, but I think that should be discussed separately.