Feature: port architecture and OS introspection support from gruntwork-install

`gruntwork-install` has the ability to introspect the OS and architecture of the system to determine which binary asset to install.

I can see why this is not in `fetch`, which is more generic and thus cannot rely on our naming conventions, but it would be nice if that functionality was baked into fetch itself. The primary use case for this would be Windows support. `gruntwork-install` is implemented in `bash`, which means it can't be used in most Windows environments. It would be nice if we can port that functionality into `fetch`, so that we can support Windows too.

Notes:

- I am not sure how to make this more generic. Perhaps we can assume our naming convention, and then if it doesn't match have an interactive prompt to select the correct one, sorting the list by name introspection?
- Alternatively, we can reimplement `gruntwork-install` to be in python or Go so that it is portable.