Add WSL Idris installation compatibility

[jmanuel1]

The use case for this PR is that I have Idris installed through Pack in WSL. (I've considered installing Idris in Windows, but Pack doesn't support Windows.) Since Idris in Linux won't understand Widows paths, something needs to translate them. VS Code has a more advanced solution to this kind of problem, but Atom and Pulsar don't.

So I'm making this PR but I figure it might warrant more discussion since:

• I'm adding a dependency, wsl-path, which is a wrapper around the wslpath tool installed in WSL distros. We could access the tool directly, but I don't think I knew it existed before I found the npm package.
• More importantly, maybe someone thinks that translating paths is outside the purview of atom-language-idris and should be dealt with some other way

[melted]

I think it makes sense to use the NPM package for convenience.