Made booleans start with a prefix, e.g. is_open
Added a leading underscore to two virtual functions
Added VIRTUAL comment above several virtual functions
Renamed accel -> acceleration in a function
Used `var variable := 0.0` as discussed in the Godot issue, instead of
`var variable: = 0.0`.
Mostly these are minor/cosmetic changes, but I've also reorganized the
folder structure (naming of folders) to reflect our guidelines, plus
made some minor changes to the demo codes. Still work in progress.