Implement JSON error emission

[breaking-change]

syntax::errors::Handler::new has been renamed to with_tty_emitter

Many functions which used to take a syntax::errors::ColorConfig, now take a rustc::session::config::ErrorOutputType. If you previously used ColorConfig::Auto as a default, you should now use ErrorOutputType::default().

src/libsyntax/parse/mod.rs

@@ -49,7 +49,7 @@ pub struct ParseSess {
 impl ParseSess {
     pub fn new() -> ParseSess {
         let cm = Rc::new(CodeMap::new());
-        let handler = Handler::new(ColorConfig::Auto, None, true, false, cm.clone());
+        let handler = Handler::with_tty_emitter(ColorConfig::Auto, None, true, false, cm.clone());
         ParseSess::with_span_handler(handler, cm)
     }