Move InMemory Provider to Rules.Framework and reference projects directly

[jdromeiro]

Description

• Reference projects within solution by project reference, instead of by package.
  This will help in further developments, as we'll not need to create multiple branches to go live with modifcations that affect both the RulesEngine and Providers. It will also force users to use versions of rulesFramework and providers that are "in agreement".
• Move the Providers.InMemory to inside the Rules.Framework assembly (so that it now makes part of the rules.framework nuget). This way, the Rules.Framework works as a standalone nuget and the user doesn't need to install two nugets when he just wants the simplest way to use the framework.

Change checklist

• Code follows the code rules guidelines of this project
• Commit messages follow the commit rules of this project
• I have self-reviewed my changes before submitting this pull request
• I have covered new/changed code with new tests and/or adjusted existent ones
• I have made changes necessary to update the documentation accordingly

Please also check the I want to contribute guidelines and make sure you have done accordingly.

Disclaimer

By sending us your contributions, you are agreeing that your contribution is made subject to the terms of our Contributor Ownership Statement

[luispfgarces]

LGTM