Improve performance in pair-replacements. Fix bug in isNotCapitalized

Remarks: 
- I couldn't build with "import com.sun.istack.internal.NotNull;", so I removed it. Sorry.
- Fixed a bug in IsNotCapitalizedWord, and added tests.
- About "wordLen < MIN_WORD_LENGTH". Ok, but we can search suggestions at least for the original misspelled word. I have done it so.