update documentation to include reticles and vector math

It's probably not very good though.

docs/system.dj

@@ -63,45 +63,96 @@ Additionally, the syntax `a | b` may be used to signify that one of the listed t
 -
   a : number
   -> number
+
+-
+  a : vector
+  -> vector
 ```
 
 `-`, when used in its unary form `-x`, returns the number `x` with the opposite sign.
+When used on vectors, returns the same vector facing the reverse direction (the individual components are negated.)
+
+This operation is not defined for colors, because it doesn't make sense to have a color with negative RGBA values.
 
 ```haku
 +
   a : number
   b : number
   -> number
+
++
+  a : vector
+  b : vector
+  -> vector
+
++
+  a : rgba
+  b : rgba
+  -> rgba
 ```
 
-`+` adds two numbers together.
+`+` adds two numbers, vectors, or colors together.
 
 ```haku
 -
   a : number
   b : number
   -> number
+
+-
+  a : vector
+  b : vector
+  -> vector
+
+-
+  a : rgba
+  b : rgba
+  -> rgba
 ```
 
-`-`, when used in its binary form `x - y`, subtracts two numbers from one another.
+`-`, when used in its binary form `x - y`, subtracts two numbers, vectors, or colors from one another.
 
 ```haku
 *
   a : number
   b : number
   -> number
+
+*
+  a : vector
+  b : vector
+  -> vector
+
+*
+  a : rgba
+  b : rgba
+  -> rgba
 ```
 
 `*` multiplies two numbers together.
+When used on vectors, it scales them component-wise.
+Likewise for colors.
 
 ```haku
 /
   a : number
   b : number
   -> number
+
+/
+  a : vector
+  b : vector
+  -> vector
+
+/
+  a : rgba
+  b : rgba
+  -> rgba
 ```
 
 `/` divides a number by another number.
+When used on vectors, it divides them component-wise.
+Likewise for colors.
 
 ```haku
 floor
@@ -324,7 +375,7 @@ The following functions are used to compare values and work with `boolean`s.
   -> boolean
 ```
 
-If `b` is `()` or `False`, `not` returns `true`.
+If `b` is `()` or `False`, `not` returns `True`.
 Otherwise it returns `False`.
 
 ```haku
@@ -459,25 +510,6 @@ vecW
 
 ---
 
-Note that mathematical operations are currently not defined for vectors.
-You may define your own vector operations like so:
-
-```haku
--- Vector addition
-addv = \a, b ->
-  vec (vecX a + vecX b) (vecY a + vecY b) (vecZ a + vecZ b) (vecW a + vecW b)
-
--- Likewise for subtraction, multiplication, and division.
-```
-
-Note that haku-defined vector operations like these are more costly the more components they operate on.
-Therefore, it's recommended to only define them for two dimensions, unless you really need more.
-
-```haku
-addv2 = \a, b ->
-  vec (vecX a + vecX b) (vecY a + vecY b)
-```
-
 ## Colors
 
 ```haku
@@ -520,6 +552,7 @@ For example, consider multiplicatively blending two colors.
 
 ```haku
 -- This is how you can multiply two colors together.
+-- Note that the `*` operator works for colors, so you don't need to define this in your brushes.
 mulRgba = \a, b ->
   rgba (rgbaR a * rgbaR b) (rgbaG a * rgbaG b) (rgbaB a * rgbaB b) (rgbaA a * rgbaA b)
 ```
@@ -539,12 +572,12 @@ mulRgba = \a, b ->
 Note that haku does not clamp colors to the `0` to `1` range.
 It is perfectly valid to have a color that is out of range or even `NaN`, but when drawing scribbles:
 
+- any number less than `0` is clamped to `0`.
+- any number greater than `1` is clamped to `1`.
 - `∞` is clamped back to `1`.
 - `-∞` is clamped back to `0`.
 - any scribble with a `NaN` color is ignored.
 
-Note that just like vectors, arithmetic operations on colors are currently not defined.
-
 Before scribbles are drawn to the wall, colors are converted to 8-bit integers for more efficient rasterization and storage.
 This means some loss of precision will happen, which may cause issues with brushes like this one:
 
@@ -625,7 +658,7 @@ stroke
 
 Creates a stroke scribble, which outlines the provided shape with a stroke of the given thickness and color.
 
-Point shapes are drawn as squares, and `line` shapes have square caps at the line's endpoints.
+Point shapes are drawn as circles, and `line` shapes have round caps at the line's endpoints.
 
 ```haku
 fill