Fix release metadata and repair the benchmarks

- repository pointed at the old host and the old repo name; this is the link
  crates.io and docs.rs display
- the readme example imported `differential_equations`, so it could not
  compile under the crate's published name
- `cargo bench` did not build: `Solution` borrows the ODE, so `.solve()`
  cannot be called on a temporary `Problem`. Bind it first.

benches/bs3_vs_dp5.rs

@@ -200,7 +200,8 @@ fn bench_interpolation(c: &mut Criterion) {
         let bs3 = BS3::new().a_tol(tol).r_tol(tol);
         b.iter(|| {
             black_box({
-                let solution = Problem::new(ode, bs3, controller).solve();
+                let mut problem = Problem::new(ode, bs3, controller);
+                let solution = problem.solve();
                 // Interpolate at 100 points
                 let _: Vec<_> = (0..100).map(|i| solution.interpolate(i as f64 * 0.05)).collect();
             });
@@ -213,7 +214,8 @@ fn bench_interpolation(c: &mut Criterion) {
         let dp45 = DormandPrince45::new().a_tol(tol).r_tol(tol);
         b.iter(|| {
             black_box({
-                let solution = Problem::new(ode, dp45, controller).solve();
+                let mut problem = Problem::new(ode, dp45, controller);
+                let solution = problem.solve();
                 // Interpolate at 100 points
                 let _: Vec<_> = (0..100).map(|i| solution.interpolate(i as f64 * 0.05)).collect();
             });

benches/simple_1d.rs

@@ -45,7 +45,8 @@ fn bench_interpolation_1d(c: &mut Criterion) {
     c.bench_function("bench_interpolation_1d", |b| {
         b.iter(|| {
             std::hint::black_box({
-                let solution = Problem::new(ode, dp45, controller).solve();
+                let mut problem = Problem::new(ode, dp45, controller);
+                let solution = problem.solve();
                 let _ = (0..100).map(|t| solution.interpolate(t as f64 * 0.1)[0]);
             });
         });