Update powershell.el recipe to maintained repo.

**Brief summary**

I combined powershell.el and powershell-mode.el.   I cleaned up the documentation and reorganized some of the code.

Your association with the package (e.g., are you the maintainer? have you contributed? do you just like the package a lot?).

The powershell.el has not been updated since 2008.  powershell-mode was last updated in October 2012.  I combined the two packages and did some basic clean-up.  I will maintain it, unless someone else wants it.

**A direct link to the package repository.**

https://github.com/jschaf/powershell.el