Change Debug to match Display

The derived `Debug` showed the raw digit data, which is sometimes useful
if you're debugging `num-bigint` itself, but annoying in many other
contexts. For something like a simple `dbg!` call in a program, you
probably just want to see the numeric value.

This is not _necessarily_ a breaking change, but we'll treat it so.

src/bigint.rs

@@ -59,7 +59,6 @@ impl Neg for Sign {
 }
 
 /// A big signed integer type.
-#[derive(Debug)]
 pub struct BigInt {
     sign: Sign,
     data: BigUint,
@@ -137,6 +136,12 @@ impl Default for BigInt {
     }
 }
 
+impl fmt::Debug for BigInt {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
 impl fmt::Display for BigInt {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.pad_integral(!self.is_negative(), "", &self.data.to_str_radix(10))

src/biguint.rs

@@ -35,7 +35,6 @@ pub(crate) use self::convert::to_str_radix_reversed;
 pub use self::iter::{U32Digits, U64Digits};
 
 /// A big unsigned integer type.
-#[derive(Debug)]
 pub struct BigUint {
     data: Vec<BigDigit>,
 }
@@ -106,6 +105,12 @@ impl Default for BigUint {
     }
 }
 
+impl fmt::Debug for BigUint {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
 impl fmt::Display for BigUint {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.pad_integral(true, "", &self.to_str_radix(10))