added travis build status and GoDoc reference link

Author: alex-alrux

README.md

@@ -4,10 +4,14 @@ This is a drop-in replacement for the standard [Go](http://golang.org) package w
 
 ## Maturity
 
+[![Build Status](https://travis-ci.org/agext/errors.svg?branch=master)](https://travis-ci.org/agext/errors)
+
 Stable: no known bugs or performance issues.
 
 ## Overview
 
+[![GoDoc](https://godoc.org/github.com/agext/errors?status.png)](https://godoc.org/github.com/agext/errors)
+
 If you need to retain more information about an error message than a single string allows, just substitute this package for the one in the standard library.
 
 The `New` function still accepts a single string as argument, so no code will be broken. Where you need to include additional information, you can provide it to `New` in a `Desc` structure instead of the string, or you can add it to the error message using one of its setter methods.