update docs

Author: mazznoer

PRESET.md

@@ -4,6 +4,20 @@ All preset gradients are in the domain [0..1]. Uniform B-splines is used to inte
 
 ![img](docs/images/rgb-plot.png)
 
+```rust
+use colorgrad::Gradient;
+
+let g = colorgrad::preset::viridis();
+
+assert_eq!(g.domain(), (0.0, 1.0));
+
+println!("{}", g.at(0.27).to_hex_string());
+
+for color in g.colors_iter(35) {
+    println!("{:?}", color.to_rgba8());
+}
+```
+
 ## Diverging
 
 `colorgrad::preset::br_bg()`

src/gradient/basis.rs

@@ -20,16 +20,17 @@ fn basis(t1: f32, v0: f32, v1: f32, v2: f32, v3: f32) -> f32 {
     feature = "named-colors",
     doc = r##"
 ```
-# use std::error::Error;
+# fn main() -> Result<(), Box<dyn std::error::Error>> {
+# use colorgrad::{GradientBuilder, BasisGradient};
 use colorgrad::Gradient;
 
-# fn main() -> Result<(), Box<dyn Error>> {
-let grad = colorgrad::GradientBuilder::new()
+let grad = GradientBuilder::new()
     .html_colors(&["deeppink", "gold", "seagreen"])
-    .build::<colorgrad::BasisGradient>()?;
+    .build::<BasisGradient>()?;
 # Ok(())
 # }
-```"##
+```
+"##
 )]
 #[derive(Debug, Clone)]
 pub struct BasisGradient {

src/gradient/catmull_rom.rs

@@ -9,16 +9,17 @@ use crate::{convert_colors, BlendMode, Color, Gradient, GradientBuilder, Gradien
     feature = "named-colors",
     doc = r##"
 ```
-# use std::error::Error;
+# fn main() -> Result<(), Box<dyn std::error::Error>> {
+# use colorgrad::{GradientBuilder, CatmullRomGradient};
 use colorgrad::Gradient;
 
-# fn main() -> Result<(), Box<dyn Error>> {
-let grad = colorgrad::GradientBuilder::new()
+let grad = GradientBuilder::new()
     .html_colors(&["deeppink", "gold", "seagreen"])
-    .build::<colorgrad::CatmullRomGradient>()?;
+    .build::<CatmullRomGradient>()?;
 # Ok(())
 # }
-```"##
+```
+"##
 )]
 #[derive(Debug, Clone)]
 pub struct CatmullRomGradient {

src/gradient/inverse.rs

@@ -1,9 +1,27 @@
 use crate::{Color, Gradient};
 
-/// A gradient that inverts the gradient of another gradient.
-///
-/// The minimum value of the inner gradient will be the maximum value of the inverse gradient and
-/// vice versa.
+#[cfg_attr(
+    feature = "preset",
+    doc = r##"
+A special gradient that inverts the inner gradient.
+
+The minimum value of the inner gradient will be the maximum value of the inverse gradient and
+vice versa.
+
+```
+use colorgrad::Gradient;
+
+let gradient = colorgrad::preset::magma();
+let inverted = gradient.inverse();
+
+assert_eq!(gradient.at(0.9).to_rgba8(), inverted.at(0.1).to_rgba8());
+
+for color in inverted.colors_iter(15) {
+    println!("{}", color.to_hex_string());
+}
+```
+"##
+)]
 #[derive(Clone)]
 pub struct InverseGradient<'a> {
     inner: Box<dyn Gradient + 'a>,

src/gradient/linear.rs

@@ -7,16 +7,18 @@ use crate::{BlendMode, Color, Gradient, GradientBuilder, GradientBuilderError};
     feature = "named-colors",
     doc = r##"
 ```
-# use std::error::Error;
+# fn main() -> Result<(), Box<dyn std::error::Error>> {
+# use colorgrad::{BlendMode, GradientBuilder, LinearGradient};
 use colorgrad::Gradient;
 
-# fn main() -> Result<(), Box<dyn Error>> {
-let grad = colorgrad::GradientBuilder::new()
+let grad = GradientBuilder::new()
     .html_colors(&["deeppink", "gold", "seagreen"])
-    .build::<colorgrad::LinearGradient>()?;
+    .mode(BlendMode::Oklab)
+    .build::<LinearGradient>()?;
 # Ok(())
 # }
-```"##
+```
+"##
 )]
 #[derive(Debug, Clone)]
 pub struct LinearGradient {