Add Appveyor and codecov badges

I would have changed the CWL conformance one to include the text inside the badge: https://img.shields.io/jenkins/s/https/ci.commonwl.org/job/cwltool-conformance.svg?label=CWL%20conformance

Unfortunately shields.io doesn't retrieve the info from Jenkins even though when queried manually the endpoint [works](https://ci.commonwl.org/job/cwltool-conformance/api/json?tree=color).

Author: psafont

README.rst

@@ -2,11 +2,21 @@
 Common Workflow Language tool description reference implementation
 ==================================================================
 
-CWL conformance tests: |Build Status| Travis CI: |Unix Build Status|
+CWL conformance tests: |Conformance Status| |Linux Status| |Windows Status| |Coverage Status|
 
-.. |Unix Build Status| image:: https://img.shields.io/travis/common-workflow-language/cwltool/master.svg?label=unix%20build
+
+.. |Conformance Status| image:: https://ci.commonwl.org/buildStatus/icon?job=cwltool-conformance
+   :target: https://ci.commonwl.org/job/cwltool-conformance/
+   
+.. |Linux Status| image:: https://img.shields.io/travis/common-workflow-language/cwltool/master.svg?label=Linux%20builds
    :target: https://travis-ci.org/common-workflow-language/cwltool
+   
+.. |Windows Status| image:: https://img.shields.io/appveyor/ci/mr-c/cwltool/master.svg?label=Windows%20builds
+   :target: https://ci.appveyor.com/project/mr-c/cwltool
 
+.. |Coverage Status| image:: https://img.shields.io/codecov/c/github/common-workflow-language/cwltool.svg
+  :target: https://codecov.io/gh/common-workflow-language/cwltool
+   
 This is the reference implementation of the Common Workflow Language.  It is
 intended to feature complete and provide comprehensive validation of CWL
 files as well as provide other tools related to working with CWL.
@@ -110,9 +120,6 @@ and ``--tmp-outdir-prefix`` to somewhere under ``/Users``::
 
     $ cwl-runner --tmp-outdir-prefix=/Users/username/project --tmpdir-prefix=/Users/username/project wc-tool.cwl wc-job.json
 
-.. |Build Status| image:: https://ci.commonwl.org/buildStatus/icon?job=cwltool-conformance
-   :target: https://ci.commonwl.org/job/cwltool-conformance/
-
 Using user-space replacements for Docker
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