Added parameter and parameter_list

parameters are to be used as placeholders in the query.
parameter lists are to be used to assign values to these parameters and
forward them to the database.
Can extract parameters from expression
select now collects parameters from Where and Having
Added a prepared_select_t type and a prepare method for select

This is not done yet, but it indicates the way to go...
Moved result construction more towards connector.

This will make it easier to handle different formats
Added default constructor to result field types
Refactored of result and result row (clearer structure depending on connectors)
Fixed bug in dynamic result row.
Parameters of prepared statements can be null now
Can now prepare a select (tested with mysql)
Can now bind integral parameters and execute prepared queries
Turned value_type::parameter_t into a non-template
Can bind results.
prepared to detemplatify connector results
Successfully running the first prepared select statement including result evaluation
Added missing validate methods
Changed data type for boolean to signed char (seems to be more common for binary bindings)
Small fix for dynamic results and a hint for positional parameters
Test with boolean and text parameters in prepared query compiles and runs

with mysql
Added static assert to prevent automatic rivial->null conversion to happen in where/having