#137 added guard clauses
installed LiteGuard.Source package into ScriptCs.Core only and linked from other projects
created ScriptCs.ruleset based on MS recommended rules and added CA1062: Validate arguments of public methods
Merge pull request #242 from adamralph/137-guard-clauses

#137 added guard clauses
Bump the version to v0.5.0-alpha
Respect the allowPreRelease flag even if no version is provided
Merge pull request #254 from jrusbatch/issues/252

Allow installation of prerelease packages without requiring a valid version to be specified.