Tests: Add code coverage

Use built in MATLAB code coverage tool to generate code coverage report.

There are two warnings when this runs for which fixes are not readily
apparent:

Warning: Coverage result is empty for check_range.m because the file is invalid.

Warning: Coverage result is empty for blade_moments.m because the file is invalid.

These two warnings indicate that code coverage is not being generated
for those files.

mhkit/tests/runTests.m

@@ -3,6 +3,9 @@
     import matlab.unittest.TestRunner;
     import matlab.unittest.TestSuite;
     import matlab.unittest.plugins.TestReportPlugin;
+    import matlab.unittest.plugins.CodeCoveragePlugin;
+    import matlab.unittest.plugins.codecoverage.CoverageReport;
+
 
     % Define test suite
     testFileName = mfilename('fullpath');
@@ -22,6 +25,14 @@
     plugin = TestReportPlugin.producingPDF(pdfFile);
     runner.addPlugin(plugin);
 
+    % Add Code Coverage Report
+    sourceCodeFolder = fileparts(testsFolder);
+    codeCoverageFolder = fullfile(testsFolder, 'coverage_report');
+    reportFormat = CoverageReport(codeCoverageFolder);
+
+    p = CodeCoveragePlugin.forFolder(sourceCodeFolder, Producing=reportFormat, IncludingSubfolders=true);
+    runner.addPlugin(p);
+
     % Run the tests
     results = runner.run(suite);