Refactor SentenceIterator tests
Enhance test for SentenceIterator
Add assertions
Modify checkstyle configuration file

- added a exception of maximum line length
Fix items pointed out by Ohtani-san's comment
Rename setHeaderContent into appendHeaderContent

- changed not to set List parameter but to adding parameter elements
Fix Javadoc
Merge pull request #90 from takahi-i/enhance-tests-for-sentenceiterator

Enhance tests for sentenceiterator