Add accessibility attributes and tags

[alvaromontoro]

The SVG files could get an accessibility boost by adding some attributes:

• Image aria role (role="img")
• Linked descriptions (aria-labelledby="[IDs]")
• Title (<title>)
• Description (<desc>)

Sources:

• Creating Accessible SVGs, by Carie Fisher at Deque
• Accessible SVGs: Perfect Patterns For Screen Reader Users, by Carie Fisher at Smashing Magazine

[argyleink]

fixed by #36