Update CONTRIBUTING.md
new quickstart

updated readme to have an up to date quickstart!
Rewrite README.md
Specify language for syntax highlighting in code blocks
Bump version number to v0.4.0
Merge branch 'master' into dev

* master:
  new quickstart
  Update CONTRIBUTING.md
#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.