probe(): returns Libraries instead of the hash directly

This is an API break.

src/lib.rs

@@ -191,15 +191,12 @@ pub enum Error {
 }
 
 #[derive(Debug, Default)]
-struct Libraries {
+/// All the system dependencies retrieved by [Config::probe].
+pub struct Libraries {
     libs: HashMap<String, Library>,
 }
 
 impl Libraries {
-    fn into_hash(self) -> HashMap<String, Library> {
-        self.libs
-    }
-
     /// Retrieve details about a system dependency.
     ///
     /// # Arguments
@@ -427,7 +424,7 @@ impl Config {
     /// `[package.metadata.system-deps]` section.
     ///
     /// The returned hash is using the the `toml` key defining the dependency as key.
-    pub fn probe(self) -> Result<HashMap<String, Library>, Error> {
+    pub fn probe(self) -> Result<Libraries, Error> {
         let libraries = self.probe_full()?;
         let flags = libraries.gen_flags()?;
 
@@ -438,7 +435,7 @@ impl Config {
             println!("cargo:rustc-cfg=system_deps_have_{}", name.to_snake_case());
         }
 
-        Ok(libraries.into_hash())
+        Ok(libraries)
     }
 
     /// Add hook so system-deps can internally build library `name` if requested by user.