Fix the line counting in string function

The line counter becomes invalid, when the rules with linewrap are
used. This issue appears, because the parsing FSM does not rollback
the line counter after attempting such rule.
Add unit test for string fun in leex test suite
Fix line counting in token and tokens functions

The line counter becomes invalid, when the rules with linewrap are
used. This issue appears, because the parsing FSM does not rollback
the line counter after attempting such rule.
Unit tests for 'token' and 'tokens' are also added.