Addition of various features (main is createOrAlterTable)

Hello,

I propose you to add this features to your library:

* createOrAlterTable
* Multiple query execution
* Limited select

New functions are:

* selectLimit(string table, object where, int limit)
* selectAllLimit(string table, int limit)
* selectOne(string table)
* executeQueries([object queries], [[object values]])
* addColumns(string tableName, object newColumns)
* createOrAlterTable(string tableName, object iColumns)