added PackageVersion arg
added new arg for package version
corrected the logic in setting package in argument parser
changed InstallCommand, CommandFactory to respect package version
package version and special version will be extracted in PackageReference
added tests
moved PackageReferenceTests to separate file
Combine Scriptcs.Contracts with ScriptCs.Contracts
Merge pull request #558 from filipw/installv

Added support for installing a specific version
Merge branch 'dev' of https://github.com/scriptcs/scriptcs into friendly-module-loader

Conflicts:
	test/ScriptCs.Tests/ArgumentParserTests.cs