(GH-563) Merge PowerShell Scripts into shippable Modules on build

[mwallner]

Description Of Changes

Added a 'INCLUDE directive' that allows to include content of arbitrary files into the Boxstarter .psm1 modules.

Previously, the modules have been shipped together with a bunch of .ps1-files that have been dot-sourced when loading the module:

Resolve-Path $PSScriptRoot\*.ps1 | % { . $_.ProviderPath }

With this changes, it's possible to do something like the following:

# --- INCLUDE *.ps1

Motivation and Context

• only need to sign the psm1 files on build
• fewer artifacts to ship
• better module-loading times

Testing

WIP / so far no issues

• choco install
• initial bootstrapping
• Install-BoxstarterPackage
• ...

Operating Systems Testing

WIP / so far no issues

• Sever 2019 (vagrant box)

Change Types Made

• Bug fix (non-breaking change).
• Feature / Enhancement (non-breaking change).
• Breaking change (fix or feature that could cause existing functionality to change).
• Documentation changes.
• PowerShell code changes.

Change Checklist

• Requires a change to the documentation.
• Documentation has been updated.
• Tests to cover my changes, have been added.
• All new and existing tests passed?
• PowerShell code changes: PowerShell v3 compatibility checked?

Related Issue

Fixes #563

[mwallner]

Not really important but also in this PR: I've added the possibility to build Boxstarter on a Linux system (given the chocolatey/choco docker image is present) - so that I can do some work on Boxstarter when I've only got my laptop with me 😄