Upgraded Microsoft NuGet packages to ver 3.1.12

Merge pull request #46 from Umplify/issue_45

Upgraded NuGet packages #45

Had service collection cleared upon disposing fixtures

Merge pull request #43 from Umplify/Issue_42

Addresssed issue #42

Upgraded Microsoft NuGet packages to version 3.1.11

Merge pull request #40 from Umplify/issue_39

Issue 39

Supporting asynchronous disposing pattern in TestBed and TestBedFixture classes

Both TestBed and TestBedFixture classes still support the IDisposable interface as well and they will continue to be in the same way. Please consult issue #30 for further details and the PR associated with that issue.

Upgraded Microsoft.NET.Test.Sdk

Bumped Microsoft.NET.Test.Sdk from 16.8.0 to 16.8.3

v1.0.50: Update azure-pipelines.yml for Azure Pipelines

IConfigurationRoot instance has become available to derived fixture classes.

v1.0.0.48: Merge pull request #22 from Umplify/issue_21

Test developers' loggers can now be added to the fixture #24