Add ability to use this package without modifying the .proj file

[bstichterCarleton]

I prefer to keep my junior programmers from digging around in project files because they tend to forget about settings and actions that are manually added there. I would like to use this package without needing to do that. I would propose that this could be done relatively easily by just changing the default for RunNuGetPack to true when in Release mode. This could be extended by adding support for a custom XML Processing Instruction in the .nuspec file to handle other settings.

[bstichterCarleton]

Created an enhancement in the above referenced pull request using the solution I proposed in the issue report.