LudvigOlsen/xpectr: xpectr 0.3.0

Breaking: element_classes() only returns the first class string per element.

Adds navigateTestFileAddin() addin for opening test file from string name. E.g. when running testthat in the build window, copy the filename and line number of the failed test, e.g. test_x.R:5:, and run the addin. It will then open /tests/testthat/test_x.R at line 5.

Adds test of class attribute for errors.

Extracts error message with conditionMessage() instead of $message.

Adds indentation = 2 to generated code from initializeGXSFunctionAddin().

Bug fix: Does not check symmetry for table objects.