Add coverage badge to README. Exclude polyfill.

.gitignore

@@ -1,2 +1,3 @@
 node_modules
-.nyc_output
+.nyc_output
+coverage

.istanbul.yml

@@ -0,0 +1,7 @@
+instrumentation:
+    root: .
+    extensions:
+        - .js
+    default-excludes: true
+    excludes: ['proxy.js','**min.js','gulpfile.js']
+    include-all-sources: true

README.md

@@ -1,9 +1,9 @@
-[![Build Status](https://travis-ci.org/ElliotNB/observable-slim.svg?branch=master)](https://travis-ci.org/ElliotNB/observable-slim)
+[![Build Status](https://travis-ci.org/ElliotNB/observable-slim.svg?branch=master)](https://travis-ci.org/ElliotNB/observable-slim) [![Coverage Status](https://coveralls.io/repos/github/ElliotNB/observable-slim/badge.svg)](https://coveralls.io/github/ElliotNB/observable-slim)
 
 # Observable Slim
 https://github.com/elliotnb/observable-slim
 
-Version 0.0.4
+Version 0.0.5
 
 Licensed under the MIT license: