Assign Version Number Based on Last Tag

[WalkerCodeRanger]

Currently, Appveyor assigns a version number based either on the tag being built, or the version number in appveyor.yml along with a build number to make it unique. Instead, find the last version tag and increment the patch by 1, then use the build number to assign a prerelease version. That way, the appveyor.yml won't need to be updated.