Refactored Tokenizer and LemmaIndexMapred. Also changed ArrayList -> HashSet in GetArticlesMapred
fixed comment in GetArticlesMapred
#10, #11: renamed WikiArticlesMR physically to PA1 to facilitate merging into master
#10, #11: merged in steven.10and11.refactoring.
Applied our new common Java Code Style (with the 100 chars line width as requested by Steven).
Closes #10.
Closes #11.