better build scripts for developers

- Maps F7 to 'build and publish PowerShell.package to *Data/Installed packages* dir'
- Adds a bunch of crude scripts meant only for developers

Requirements:

(This is a primitive build system, but it's efficient.)

First, you need to create a file at `~` called `.sublime-package-dev` with
these contents:

```
global-win editor ~/utilities/Sublime Text 3/sublime_text.exe
global-win installed-packages ~/utilities/Sublime Text 3/Data/Installed Packages
```

Open PowerShell.sublime-project file as a project.
Select 'Run' from the Tools/Build System menu.

Your PowerShell local repo should be outside of the Sublime Text
Packages folder. From now on, Sublime Text will be using
<Data>/Installed Packages/PowerShell.sublime-package.

This matches more closely to what the users will end up with in
their local installation of Sublime Text (IIRC).

Regardless, this adds a bunch of files that are simply clutter
to users, but I'm not aware of any way of solving that problem
short of creating separate repos for development and deployment.