docs: Add code conventions

[faretek1]

Add name conventions e.g.

PascalCase: struct, enum, struct constructor macro
snake_case: var, list, broadcast, costume, proc, func, %include, sprite
SCREAMING_SNAKE_CASE: macro (%define)

Also add conventions like code ordering

%include inflator/cmath

%define PI_YAY 3.14159265358979323

costumes "blank.svg";
sounds "meow.wav";

struct Vec2 {
	x, y
}

%define Vec2(x, y) (Vec2{x: x, y: y})

proc main {
	Vec2 v = Vec2(1, 2);
	log v.x & ", " & v.y;
	log PI_YAY & " is cool!";
}

onflag {
	main;
}

i.e.

1. includes & macros for compile time library customisation
2. Const macros
3. costumes and sounds
4. general macros
5. structs
6. procs & funcs
7. onflag and other hat blocks

[faretek1]

In addition, a convention for doc commenting of procs/macros/structs/funcs like JSDoc would be useful, as you said earlier