(#172) Altered way that GitVersion is installed

- Rather than have GitVersion.exe in the Tools folder, lets install it as part of build process
- Deleted GitVersion.exe from Tools folder
(#172) Change installation source for GitVersion

- Temporarily use the hooky installation source for GitVersion which comes from my MyGet feed
- This has the result of Pull Request https://github.com/Particular/GitVersion/pull/262
(#172) Removed artifact publishing from yml file

- This will instead be done within the psake build script
(#172) Added nuget package caching

- Now that the Pull Request issues in AppVeyor have been correct, we can add back in the nuget package caching, which should speed up the build somewhat.
(#172) Completed GitVersion, added StyleCop and CodeAnalysis

- When running in AppVeyor, run GitVersion with /output buildserver and read environment variable to get LegacySemVer version number
- When not running in AppVeyor, call GitVersion directly, and parse the JOSN output to get the LegacySemVer version number
- Added Analysis of StyleCop Errors, and publishing of StyleCop report
- Added Analysis of Code Analysis Errors, and publishing of Code Analysis report