- MysqliDb::insertMulti() requires at least a table-name and
two-dimensional array containing the data-sets
- the third parameter $dataKeys can contain an array, setting|overriding
the table column names in the data-sets
- removes some unnecessary linebreaks and comments
- fixes typo
- adds insertMulti() to Readme
- adds MysqliDB::insertMulti() insertion tests
- removes whitespace changes