fix #6161
Correct singular/plural mismatch
Merge pull request #6166 from catawbasam/patch-1

Correct singular/plural mismatch
Windows CI using AppVeyor

New configuration file appveyor.yml
- Downloads and installs latest Julia binary, uses it for dependency libraries
- Also uses MSYS from bundled Git installation

Build script contrib/windows/msys_build.sh
- Downloads MinGW, LLVM, make, etc
- Sets up Make.user to use as many downloaded dependencies as possible