Update handlebars to 3.0 which included performance improvements.

Updated lettre to newer git revision, which should give better error messages now.

src/error.rs

@@ -46,6 +46,7 @@ use std::option::NoneError as NoneErr;
 use std::time::SystemTimeError as TimeErr;
 use u2f::u2ferror::U2fError as U2fErr;
 use yubico::yubicoerror::YubicoError as YubiErr;
+use lettre::smtp::error::Error as LettreErr;
 
 #[derive(Display, Serialize)]
 pub struct Empty {}
@@ -73,6 +74,7 @@ make_error! {
     ReqError(ReqErr):     _has_source, _api_error,
     RegexError(RegexErr): _has_source, _api_error,
     YubiError(YubiErr):   _has_source, _api_error,
+    LetreErr(LettreErr):  _has_source, _api_error,
 }
 
 // This is implemented by hand because NoneError doesn't implement neither Display nor Error