Globber Relative Path Fix
Fixes issue in Cake.Core.IO.Globber.Walk() resulting some relative
paths would result in below exception
 startIndex cannot be larger than length of string.

This because the relative rootpath could be longer/different vs.
child file/folder paths.

I.e. this would fail:
..\cake\src\Cake\bin\Debug\Cake.exe .\build.csx -solution="..\Cake\src\Cake.sln"

Fix uses the PathCollapser.Collapse() to clean up the full root path
causing the issue.
Changed version number.
Suppressed xUnit test count on non local builds.
Merge https://github.com/cake-build/cake into globberfix
Merge pull request #104 from devlead/globberfix

Globber relative path fix.
Disabled test discovery in AppVeyor.
Publish Cake to MyGet.
Skip publishing for pull requests.
Use latest CI build from MyGet when building Cake.
Added uploading of test results.
Added uploading of artifacts.
Specifying a script should take precedence over version or help commands. Closes #102.
Throw if target cannot be reached due to constraints. Closes #106.
Log when tasks are skipped.
Changed location of transformed nuspec file. Closes #110.
Made nuspec XML namespaces optional. Closes #109.
Increased version number to 0.1.20.