Sprite SVG

[mdo]

Builds on and replaces #262 with several changes:

• Updates docs a smidge around using sprites
• Replaces homepage grid of icons with sprite; cut around 30% of page file size according to my quick math
• Adds sprite SVG to the npm package
• Moves sprite generation to before the site build

[XhmikosR]

This is using obsolete dependencies...

[XhmikosR]

@mdo Also, SVGO does not seem to run for the sprite image?

EDIT: NVM, I see SVGO is the default svg-sprite transform :) Although, not sure what config it's using, but if it works, it works.

EDIT2: What I don't like is that we load another huge file on page load...