add fancy appveyor badge

Author: adswa

README.md

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 [![codecov](https://codecov.io/gh/AdinaWagner/multimatch/branch/master/graph/badge.svg)](https://codecov.io/gh/AdinaWagner/multimatch)
 [![Documentation](https://readthedocs.org/projects/multimatch/badge/?version=latest)](https://multimatch.readthedocs.io/en/latest/)
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 # multimatch
 ## Reimplementation of MultiMatch toolbox (Dewhurst et al., 2012) in Python.