- examples/EBNF: new ebnf example

examples/EBNF/grammar_tests/01_test_leaf_elements.ini

+[match:symbol]
+M1: word
+M2: one_word_with_underscores
+
+[fail:symbol]
+F1: two words
+

examples/EBNF/grammar_tests/02_test_document.ini

+[match:document]
+M1: """This is a sequence of words
+    extending over several lines"""
+M2: """  This sequence contains leading whitespace"""
+
+[fail:document]
+F1: """This test should fail, because neither
+    comma nor full have been defined anywhere."""