Updates README

Updates test cases

Removes the management of the value "NOW()"

Fixes getColumns() throws bound error with MySQL

Adds caching capabilities and security warning

Adds security warnings in doc blocks

Adds support for charset connection

Add literals and mysql tests

Add support for literals + minor changes

Add helper Db::literal()

Fix NULL assignment in Table::restore()

Fix return statement error for DELETE queries

Add Table ability to define columns types bindings

Minor fixes

Add hooks before and after query execution