added PS script to ReactiveUI-Core\tools for scaffolding
The init.ps1 should be called on install and subsequent
solution loads by NuGet Package Manager in Visual Studio, per
their documentation. This script loads a PowerShell script module
that sets up the generator command (Generate-RxUIObjects) and
tab expansion for the template type argument of the same.

The generator searches subdirectories for the RxUIModelGenerator
executable and errors if it cannot be found.

A small change was necessary to the Program.cs of the CLI generator
as I could not find a way to prevent PowerShell from sending the
name of the invoked executable as the first argument to the exe
itself.  I'm not a PS expert, so there may be a way.  In any event
the change required was minimal; hopefully it passes muster.

All testing was done manually.  I did not create a nuget package
and install it to ensure that the init was called as their docs
state, but I did invoke it from the Package Manager Console and
ensure that the generator worked as expected.
changed ps module to utf8
encoding ps module as ansi
changed name of scaffolding function and gave it an alias
per @dahlbyk in
https://github.com/reactiveui/ReactiveUI/pull/309#issuecomment-18650943
Merge pull request #309 from casnap/rxui5-master

added PS script to ReactiveUI-Core\tools for scaffolding