Parsing tests skip some features

[ageorgou]

The parser tests for some ATF features are missing meaningful assertions and therefore pass trivially.

This is because these tests were initially skipped while the relevant features were not supported, but no assertions were provided when they were reenabled.

The features in question and corresponding tests in test_atfparser.py are:

Feature	Test functions
#key	test_key_protocol, test_double_equals_in_key_protocol, test_many_equals_in_key_protocol, test_empty_key_in_key_protocol
use mylines	test_mylines_protocol
use lexical	test_lexical_protocol
#lemmatizer	test_lemmatizer_protocol
={	test_line_equalsbrace

[rillian]

Since #85 these tests are marked as explicit skips again. They should be updated once there's model support for the missing features.