Switch to codecov from coveralls

Note that we install coverage<4.0 in travis because test-requirements.txt is
installing the same in the tox environments. The .coverage file format
changed in 4.0.

.codecov.yml

@@ -0,0 +1 @@
+comment: off

.travis.yml

@@ -1,5 +1,6 @@
 sudo: false
 language: python
+
 matrix:
   include:
     - python: '2.7'
@@ -12,19 +13,25 @@ matrix:
       env: TOXENV=pypy
     - env: TOXENV=flake8
     - env: TOXENV=checkspelling
+
 addons:
   apt:
     packages:
     - libtidy-0.99-0
     - aspell
     - aspell-en
+
 install:
   - pip install tox
-  - pip install coveralls
+  - pip install 'coverage<4.0'
+  - pip install codecov
+
 script:
   - tox
+
 after_success:
-  - coveralls
+  - codecov
+
 branches:
   only:
     - master

README.md

@@ -2,7 +2,7 @@
 ===================
 
 [![Build Status](http://img.shields.io/travis/Python-Markdown/markdown.svg)](https://travis-ci.org/Python-Markdown/markdown)
-[![Coverage Status](https://img.shields.io/coveralls/Python-Markdown/markdown.svg)](https://coveralls.io/r/Python-Markdown/markdown?branch=master)
+[![Coverage Status](https://codecov.io/gh/Python-Markdown/markdown/branch/master/graph/badge.svg)](https://codecov.io/gh/Python-Markdown/markdown)
 [![Latest Version](http://img.shields.io/pypi/v/Markdown.svg)](http://pypi.python.org/pypi/Markdown)
 [![Python Versions](http://img.shields.io/pypi/pyversions/Markdown.svg)](http://pypi.python.org/pypi/Markdown)
 [![BSD License](http://img.shields.io/badge/license-BSD-yellow.svg)](http://opensource.org/licenses/BSD-3-Clause)