Add standalone InvokeBuild tasks

[pauby]

The psake to InvokeBuild conversion is problematic so a standalone InvokeBuild tasks script has been added.

Description

• Added a standalone IB.tasks.ps1 InvokeBuild tasks script;
• Disabled the psake -> InvokeBuild tasks conversion in the build;
• Amended the InvokeBuild Pester test description;

Related Issue

#16

Motivation and Context

The psake conversion is problematic. It was agreed in #16 that the InvokeBuild tasks should be standalone for the time being.

How Has This Been Tested?

The InvokeBuild tasks used are the ones created by the conversion script in the last version - with a couple of fixes to the Assert statement in the Publish task (which did not work in InvokeBuild) and also to fix the Build task to allow it to use $PSBPreference.Build.Dependencies which didn;t work for InvokeBuild.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[devblackops]

Thanks @pauby! Sorry I sat on this for so long.