Add `antigravity`, `love`, and `this` modules from v1

[microbit-carlos]

• Added the XKCD antigravity comic in ASCII form (2) bbcmicrobit/micropython#181
• Easter egg love module bbcmicrobit/micropython#32
• Create a "this" module and update help bbcmicrobit/micropython#4

[dpgeorge]

Done in ea28ef4, 3c9983e and 8e5eda1