(#39) Add rule for validating underscore in ID

[AdmiringWorm]

Description Of Changes

This implements the note rule CPMR0070 that validates that a package identifier does not contain an underscore.

Motivation and Context

To improve the areas that this extension covers compared to package validator.

Testing

1. Run choco new test_package.
2. Update the nuspec content by removing all template values.
3. Update required fields to have a valid value (Version, ProjectUrl, Description, etc).
4. Attempt to run choco pack on the nuspec file.
5. Ensure that the rule CPMR0070 is flagged and shown in the console.

Operating Systems Testing

• Windows 10

Change Types Made

• [ ] Bug fix (non-breaking change).
• [x] Feature / Enhancement (non-breaking change).
• [ ] Breaking change (fix or feature that could cause existing functionality to change).
• [ ] Documentation changes.
• [ ] PowerShell code changes.

Change Checklist

• [x] Requires a change to the documentation.
• [ ] Documentation has been updated.
• [x] Tests to cover my changes, have been added.
• [x] All new and existing tests passed?
• [ ] PowerShell code changes: PowerShell v3 compatibility checked?

Related Issue

Fixes #39

[AdmiringWorm]

documentation PR created at: https://github.com/chocolatey/docs/pull/1033

[gep13]

@AdmiringWorm thanks for getting this added!