Rename ParseUtil into SentenceExtractor

- made static methods into non static
Change the SentenceExtractor constructor to have a full stop character as the parameter

- given full stop character is stored as the member variable
Add getSentenceEndPosition to SentenceExtractor
Make the constructor of SentenceExtractor to have list of end of sentence characters

- removed the period parameter from SentenceExtractor.getSentencePosition
- make PlainTextParser not use StringUtils methods

NOTE: this version only uses the first element of end of sentence character to detect
end of the sentence.
Add constructEndSentencePattern method in SentenceExtractor
Implement StringUtils.getSentenceEndPosition with Pattern
Activate pattern based sentence detector method and fixed a bug of the method
Support exclamation mark and question mark as the end of sentence
Remove character based getSentencePosition method
Fix styles

This update fix the warning of Checkstyle and remove unused variables and methods.
Merge pull request #98 from takahi-i/support-various-full-stop

Support various end of sentence characters