Add ability to create y axis tick labels

[CloverLeaf5]

This Pull Request uses the Builder Pattern modeled in #47 to give the user the ability to add sparse or dense labeling of ticks along the y-axis. The same could not be done with the x-axis due to the text direction.

An example and plot are shown below:

Chart::new_with_y_range(200, 50, 0.0, 90 as f32, 0.0, 25_000.0)
        .linecolorplot(&Shape::Continuous(Box::new(|x| 1000.0 * (5.0 * (0.5 * x).sin() + 0.05 * x) + 9000.0)), rgb::RGB { r: 10, g: 100, b: 200 })
        .x_label_format(LabelFormat::Custom(Box::new(move |val| {format!("{}", chrono::Local::now().date_naive() + chrono::Duration::days(val as i64))})))
        .y_label_format(LabelFormat::Value)
        .y_tick_display(TickDisplay::Sparse)
        .nice();

A TickDisplayBuilder trait gives Chart a y_tick_display() method for the user to specify the use of tick labels on the y-axis. Calling this method also slightly alters the height of the frame to give better accuracy of positioning and spacing between the labels.

/// Specifies density of labels on the Y axis between ymin and ymax.
/// Default value is `TickDisplay::None`.
pub enum TickDisplay {
    /// Tick labels are not displayed.
    None,
    /// Tick labels are sparsely shown (every 4th row)
    Sparse,
    /// Tick labels are densely shown (every 2nd row)
    Dense,
}

[loony-bean]

Thanks, this is looking good! Just added few comments about style

[CloverLeaf5]

I updated the Display segment of the update to better match the codebase style and better handle the Vec indexing Option.

[loony-bean]

Also please update the PR description using new names :)

[CloverLeaf5]

I added the line to the label.rs example as well, if that's alright?

[CloverLeaf5]

I see it up on crates.io! Thanks.
I apologize, it looks like I missed renaming one of the symbols in the doc comment about the enum, line 189

[loony-bean]

I see it up on crates.io! Thanks. I apologize, it looks like I missed renaming one of the symbols in the doc comment about the enum, line 189

Ah, no worries, I will fix it later. Thanks for the PR!

[CloverLeaf5]

Of course. Happy to contribute!

[CloverLeaf5]

Just an FYI - https://docs.rs/textplots/latest/textplots/ still shows the out of date YAxisTickFormat::None under Enums.