Tests: Create shared fixture module #97
Description
Create a minimal skeleton module at tests/fixtures/TestModule/ (a bare .psm1 + .psd1) to be shared across all integration tests.
This is a prerequisite for the Build-PSBuildModule, Build-PSBuildMarkdown, Build-PSBuildMAMLHelp, Build-PSBuildUpdatableHelp, Test-PSBuildPester, and Publish-PSBuildModule sub-tasks.
Parent issue: #17