Add Jitter [JITT]

[emmamarichal]

# JITT based on https://github.com/Gissio/font_Tiny5
tag: "JITT"
display_name: "Jitter"
min_value: 0
default_value: 0
max_value: 100
precision: 0
fallback {
  name: "Default"
  value: 0.00
}
fallback_only: false
description: "Controls the amount of jitter applied to the glyphs. Higher values emulate the mechanical imperfection and displacement of vintage printers."

• added .textproto
• added image

cc @davelab6 @tphinney @evanwadams