Merge #71: Add Config::builder method

aea9da2 Add `Config::builder` method (志宇)

Pull request description:

  The intention is to reduce some confusion on how to manipulate `Config`.
  The alternative is to make `Config` fields public.

ACKs for top commit:
  afilini:
    ACK aea9da2

Tree-SHA512: 4077e821260c8f6e4bc32a66548e11b1091d384988b392c981102dc3c198a5040831c5feb13b1f7b1a88fd3890d7c44c7516b94f4c2e9cbbc551581c8c72d803

src/config.rs

@@ -116,6 +116,10 @@ impl Config {
     pub fn validate_domain(&self) -> bool {
         self.validate_domain
     }
+
+    pub fn builder() -> ConfigBuilder {
+        ConfigBuilder::new()
+    }
 }
 
 impl Default for Config {