Setting y-min to 0 in relevant xan plot scenarios

Fix #348

src/cmd/plot.rs

@@ -472,6 +472,11 @@ pub fn run(argv: &[&str]) -> CliResult<()> {
         }
         if let Some(y_min) = flag_y_min {
             series.set_y_min(y_min);
+        } else {
+            // If y domain is positive, we set min to 0
+            if matches!(series.y_domain(), Some((y_min, _)) if y_min.as_float() > 0.0) {
+                series.set_y_min(DynamicNumber::Integer(0));
+            }
         }
         if let Some(y_max) = flag_y_max {
             series.set_y_max(y_max);

src/scales.rs

@@ -238,7 +238,7 @@ impl Conversion {
 }
 
 #[derive(Debug)]
-struct Scale {
+pub struct Scale {
     input_domain: (f64, f64),
     output_range: (f64, f64),
     conversion: Conversion,
@@ -325,6 +325,7 @@ mod tests {
             ticks(0.0, 10.0, 10),
             [0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0]
         );
+        assert_eq!(ticks(-5.0, 5.0, 3), vec![-5.0, 0.0, 5.0]);
     }
 
     #[test]