Handshake mascot artwork and lore

Upstream: https://github.com/mina-issho/mascots
Story: https://github.com/mina-issho/mascots/blob/master/Allison.md
License: GNU General Public License version 3 (see LICENSE.txt).

The following original PNG source artwork is included unchanged, with local filenames:
allison.png: assets/allison_20190405.png
mina.png: assets/CHIBI_20190405.png
mina-avatar.png: assets/MINA_20190405.png
bob.png: assets/bob_20190405.png

Original files: https://github.com/mina-issho/mascots/tree/master/assets
Credit: mina-issho/mascots contributors. No endorsement is implied.
Background article: https://skyinclude.com/blog/handshake-mascot/

Bob's Name Quest adds an original arcade adventure and chapter text inspired by
the mascot lore. These game events are an adaptation, not historical claims
about Handshake and not additions to the upstream story's canon.