Add missing function with_style to the Builder

It's impossible to select desired style when cbindgen is configured from
the build script.

src/bindgen/builder.rs

@@ -6,7 +6,7 @@ use std::path;
 
 use crate::bindgen::bindings::Bindings;
 use crate::bindgen::cargo::Cargo;
-use crate::bindgen::config::{Braces, Config, Language};
+use crate::bindgen::config::{Braces, Config, Language, Style};
 use crate::bindgen::error::Error;
 use crate::bindgen::library::Library;
 use crate::bindgen::parser::{self, Parse};
@@ -138,6 +138,12 @@ impl Builder {
         self
     }
 
+    #[allow(unused)]
+    pub fn with_style(mut self, style: Style) -> Builder {
+        self.config.style = style;
+        self
+    }
+
     #[allow(unused)]
     pub fn include_item<S: AsRef<str>>(mut self, item_name: S) -> Builder {
         self.config
@@ -342,3 +348,16 @@ impl Builder {
         .generate()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn with_style() {
+        assert_eq!(
+            Style::Tag,
+            Builder::new().with_style(Style::Tag).config.style
+        );
+    }
+}