8 new icons! (+fixes)

• Merge pull request #5 from halfmage/viewbox-fix 26a7418
• added 8 new icons 20e4933 (ab-testing, cake, file-off, mail-off, mood-happy, mood-neutral, mood-sad, notification-off)
• more readme updates a78cf55
• updated readme and cover 0fdd361
• added pixelarticons-icon 3e81a3b
• users.svg viewBox fix c4a4161

v1.3.1-0...v1.4.0