Logo: Fine-tune logo, add a optimized SVG file

- Complete redraw with pixel alignment by design
- Use a image size of 1024 x 1024px
- Base logo alignments on iOS 7 icon grid
- Use background corner rounding of 48px
- Optimize SVG file with svgo tool (minification)

docs/logo.svg

+<svg xmlns="http://www.w3.org/2000/svg" version="1" viewBox="-459 -463 1024 1024"><path d="M565 513c0 26-22 48-48 48h-928c-26 0-48-22-48-48v-928c0-26 22-48 48-48h928c26 0 48 22 48 48v928z" fill="#1E1E1E"/><path d="M408 34L290-130c-6-8-20-15-30-15H16c-10 0-23 7-29 15l-33 45L40 34c3 4 5 10 5 15s-2 11-5 15l-86 119 33 45c6 8 19 15 29 15h244c10 0 24-7 30-15L408 64c3-4 5-10 5-15s-2-11-5-15zM206-90c12 0 21 9 21 21s-9 21-21 21-21-9-21-21 9-21 21-21z" fill="#FFF"/><path d="M3 49c0 6-2 11-5 15l-119 164c-6 8-20 15-30 15h-146c-7 0-11-3-11-8 0-2 1-5 3-7l130-179-130-179-3-7c0-5 4-8 11-8h146c10 0 24 7 30 15L-2 34c3 4 5 10 5 15z" fill="#fff"/></svg>
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