Parser

- Now that all (?) Parser methods for tree scanning can be called more than
  once, move all methods into the ::parse method.
Parser

- ::findAttributeModifier now tolerates missing values and generates the
  correct expression term.
Unit Tests

- Removed useless setup/teardown tests.
Unit Tests

- Removed useless setup/teardown tests.
Unit Tests

- Updated recurrence period to an ISO8601 value.
- Removed useless setup/teardown tests.