FIX: Remove extra generics in Slice::new

Just to be very conservative, scale this use of Option<isize> back. I'm
not fond of this solution for overloading, it feels like it doesn't
scale. ndarray is complicated enough on the whole, let's keep each part
as simple as possible.

src/slice.rs

@@ -29,19 +29,16 @@ use super::{Dimension, Ixs};
 /// The Python equivalent is `[a::-1]`.
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 pub struct Slice {
-    pub start: Ixs,
-    pub end: Option<Ixs>,
-    pub step: Ixs,
+    pub start: isize,
+    pub end: Option<isize>,
+    pub step: isize,
 }
 
 impl Slice {
-    pub fn new<I>(start: Ixs, end: I, step: Ixs) -> Slice
-    where
-        I: Into<Option<Ixs>>,
-    {
+    pub fn new(start: isize, end: Option<isize>, step: isize) -> Slice {
         Slice {
             start,
-            end: end.into(),
+            end,
             step,
         }
     }

tests/array.rs

@@ -252,7 +252,7 @@ fn slice_oob()
 #[test]
 fn slice_axis_oob() {
     let a = RcArray::<i32, _>::zeros((3, 4));
-    let _vi = a.slice_axis(Axis(0), Slice::new(0, 10, 1));
+    let _vi = a.slice_axis(Axis(0), Slice::new(0, Some(10), 1));
 }
 
 #[should_panic]