Turn old NpmHelper into a Fake 5 module

[severisv]

#1271

[severisv]

I'm a little confused by this (from https://fake.build/contributing.html):

In order, to have a more consistent API we propose to always use camelCase naming for functions

So I implemented the API in camelCase, but looking at the rest of the Fake API, PascalCase seems to be what's used.

[matthid]

In order, to have a more consistent API we propose to always use camelCase naming for functions

Yes we have to decide for something. However it is quite difficult for some reasons:

• .NET APIs have PascalCase consistently, and we don't duplicate all of them (but we integrate into them, for example File and Directory module)
• F# APIs (FSharp.Core) have camelCase

We decided for the latter but are not 100% consistent for various reasons (for example history ones). Please feel free to send PRs to fix them.

Btw your PR looks very good, thanks!

[matthid]

Thanks a lot for taking care of this.