Introduce MSTest Support

[bryanbcook]

This PR introduces basic support for MS Test TRX format:

<TestRun xmlns="http://microsoft.com/schemas/VisualStudio/TeamTest/2010">
  <Results>
    <UnitTestResult testId="..." duration="..." outcome="...">
      <Output>
        <ErrorInfo>
          <Message>...</Message>
          <StackTrace>...</StackTrace>
        </ErrorInfo>
       </Output>
    </UnitTestResult>
    <UnitTestResult .../>
  </Results>
  <TestDefinitions>
    <UnitTest name="..." id="...">
      <TestCategory>
        <TestCategoryItem TestCategory="..." />
      </TestCategory>
      <!-- Note Properties are supported by the Schema but are not emitted on all platforms -->
      <Properties>
        <Property>
          <Key>...</Key>
          <Value>...</Value>
        </Property>
      </Properties>
      <TestMethod className="..." name="..." />
    </UnitTest>
    <UnitTest .../>
  </TestDefinitions>
</TestRun>

Known issues:

• %VSInstallDir%/Xml/Schemas/vstst.xsd defines multiple data types under /TestRun/Results.

  Element Type	Supported
  UnitTestResult	Yes
  GenericTestResult	No
  ManualTestResult	No
  WebTestResult	No
  LoadTestResult	No

• %VSInstallDir%/Xml/Schemas/vstst.xsd defines multiple data types under /TestRun/TestDefinitions:

  Element Type	Supported
  UnitTest	Yes
  UnitTestElement	Deprecated
  ManualTest	No
  WebTest	No
  CodedWebTest	No
  OrderedTest	No
  LoadTest	No
  GenericTest	No

• Although Properties are defined in the schema, they are not emitted by Visual Studio. see https://github.com/microsoft/vstest/issues/2480

• Could not replicate a test that had an "Error", so errors count on testresult and testsuite will always be empty. Invalid tests that cannot be run are not included in the test output, and details regarding their load failure are listed as plain-text in the ResultSummary element.

• Test durations are currently not calculated. #43

Support for the elements listed above could be introduced if we had sample xml (trx) outputs.

[czimbortibor]

Any chance this gets published in a new release?

[bryanbcook]

Waiting on @ASaiAnudeep re #48

[bryanbcook]

@czimbortibor a new release was pushed earlier today.

[czimbortibor]

Awesome! Thank you very much for this great tool. Appreciated