drop appveyor CI

we should move to github actions for windows

README.md

@@ -1,5 +1,4 @@
 [![Build Status](https://secure.travis-ci.org/KWARC/rust-libxml.png?branch=master)](http://travis-ci.org/KWARC/rust-libxml)
-[![Build status](https://ci.appveyor.com/api/projects/status/77y239qifm940bpu/branch/master?svg=true)](https://ci.appveyor.com/project/dginev/rust-libxml/branch/master)
 [![API Documentation](https://img.shields.io/badge/docs-API-blue.svg)](http://KWARC.github.io/rust-libxml/libxml/index.html)
 [![License](http://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/KWARC/rust-libxml/master/LICENSE)
 [![crates.io](https://img.shields.io/crates/v/libxml.svg)](https://crates.io/crates/libxml)
@@ -48,4 +47,4 @@ C:\> setx /M PATH "%PATH%;c:\vcpkg" && setx VCPKGRS_DYNAMIC "1" /M
 C:\> refreshenv
 C:\> vcpkg install libxml2:x64-windows
 C:\> vcpkg integrate install
-```
+```