Support formatting of typed names

Treat a "typed name" similarly to how we treat named arguments in argument
lists. The only exception being that we add a space after the colon.
diff --git a/CHANGELOG b/CHANGELOG
index ce64c5e..cc37458 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -2,6 +2,12 @@
 # All notable changes to this project will be documented in this file.
 # This project adheres to [Semantic Versioning](http://semver.org/).
 
+## [0.12.0] UNRELEASED
+### Added
+- Support formatting of typed names. Typed names are formatted a similar way to
+  how named arguments are formatted, except that there's a space after the
+  colon.
+
 ## [0.11.1] 2016-08-17
 ### Changed
 - Issue #228: Return exit code 0 on success, regardless of whether files were