more sonar identified stuff cleaned
removed some unused imports
dev-mysql: JSqlParser support for mysql
Quote Maven related things in Readme.md
Add a pure grammar file;
Modify SimpleQuery.java
mv PureGrammar.jj to root to keep maven correct
Update PureGrammar for further dev;
Support multi delete;

Further work:
  Use JUnit to write tablename finder & test code
  Modify the grammar file to fit mysql sql statement
Update PureGrammar.jj
Update select/delete in puregrammar.jj
update two jj files
update jj file structure
update JSqlParserCC.jj
add sections guide in JSqlParserCC.jj