Reduce the exposed functions when compare feature is enabled.

src/types/mod.rs

@@ -64,5 +64,5 @@ pub use object::Target;
 pub use object::Timestamp;
 pub use object::Underline;
 pub use object::Verbatim;
-pub use source::SetSource;
+pub(crate) use source::SetSource;
 pub use source::Source;

src/types/source.rs

@@ -1,6 +1,6 @@
 pub trait Source<'s> {
     fn get_source(&'s self) -> &'s str;
 }
-pub trait SetSource<'s> {
+pub(crate) trait SetSource<'s> {
     fn set_source(&mut self, source: &'s str);
 }