added nuget -install and command factory
added command tests,
Merge branch 'dev' of https://github.com/scriptcs/scriptcs into dev

Conflicts:
	src/ScriptCs/Program.cs
added support for local nuget.config
committing missing tests
Merge #130

Conflicts:
	src/ScriptCs/Program.cs
Support for ScriptCS files that only contain a #load.

If a file only contains #load lines, the firstCode variable will be -1, so the file was never loaded. Now this scenario will be supported.
Merge pull request #139 from PaulStovell/dev

Support for ScriptCS files that only contain a #load
Merge pull request #131 from filipw/dev

nuget -install & package validation