add hints from solution (+ clippy fixes) (#23)

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "cp_sat"
-version = "0.3.0"
+version = "0.3.1"
 edition = "2018"
 description = "Rust bindings to the Google CP-SAT constraint programming solver."
 documentation = "https://docs.rs/cp_sat"

build.rs

@@ -7,10 +7,10 @@ fn main() {
     )
     .unwrap();
 
-    if !std::env::var("DOCS_RS").is_ok() {
+    if std::env::var("DOCS_RS").is_err() {
         let ortools_prefix = std::env::var("ORTOOLS_PREFIX")
             .ok()
-            .unwrap_or("/opt/ortools".into());
+            .unwrap_or_else(|| "/opt/ortools".into());
         cc::Build::new()
             .cpp(true)
             .flag("-std=c++17")

src/builder.rs

@@ -624,6 +624,28 @@ impl CpModelBuilder {
         }
     }
 
+    /// Delete all solution hints.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use cp_sat::builder::CpModelBuilder;
+    /// # use cp_sat::proto::CpSolverStatus;
+    /// let mut model = CpModelBuilder::default();
+    /// let x = model.new_int_var([(0, 100)]);
+    /// let y = model.new_bool_var();
+    /// model.add_hint(x, 42);
+    /// model.add_hint(y, 1);
+    /// model.del_hints();
+    /// model.add_hint(x, 75);
+    /// model.add_hint(y, 0);
+    /// let response = model.solve();
+    /// assert_eq!(response.status(), CpSolverStatus::Optimal);
+    /// ```
+    pub fn del_hints(&mut self) {
+        self.proto.solution_hint = None;
+    }
+
     /// Sets the minimization objective.
     ///
     /// # Example
@@ -914,7 +936,7 @@ impl<V: Into<IntVar>> From<(i64, V)> for LinearExpr {
             res.vars.push(var.0);
             res.coeffs.push(coeff);
         }
-        return res;
+        res
     }
 }
 impl<V: Into<IntVar>, const L: usize> From<[(i64, V); L]> for LinearExpr {