test_atfparser: Mark incomplete tests with TODO.
test_atfparser: Mark incomplete tests with TODO.

These tests include atf snippets for features which the lexer
accepts, but the parser currently skips. They were marked with
a commented-out @skip decorator. With the migration to pytest
these should become @pytest.skip instead.

Instead I moved the annotation to a TODO comment, mostly because
I like the style better. I also added basic asserts on the parser
result to silence warnings.

For an example of the '={' atf syntax, see the sample corpus, and
e.g. http://oracc.iaas.upenn.edu/saao/saa10/P334031/html

UCL/pyoracc